Planescape Torment. Has all the points you are looking for, and it's on gog.

Gaming at work, eh? Don't worry, we won't tell. ;)

Games used to have boss keys.

Bump before sleep. Hopefully I start playing something tomorrow :)

Lords of the Realm 2. Great straight-forward turn-based strategy game. Doesn't really have a storyline but its engaging gameplay regardless. I think its a good choice for a more casual play schedule.

Other suggestions were great too such as Heroes of Might & Magic 3 (adds some RPG) but it can get pretty long, or Colonization a fantastic little game that I love to death.

I'm always partial to the Ultima games but if you want one that's a little more bite-sized than the excellent Ultima 7 then I would suggest Ultima 5, 6, Worlds 1, 2 or Underworld 1, 2. Most of those should be well under 100 hours and have some meatier stories but not be novels like the Interplay games of the 90s (Baldur's gate, Fallout, etc.)

If you like hack n slash RPGs then you can't go wrong with Torchlight and that's about as easy as it can get for a pick up and play and put away type gameplay.

Just ... Just get Disciples 2 and be done with it.

Oh, you own all of that. Well I should start pulling some obscure stuff, shouldn't I?

All right then, how about Original War? "But that's an RTS!" Well yeah, just bear with me. And trust me, the game is quite simply brilliant. So I'll just go ahead and run down your points:

* Preferably RPG or turn-based strategy - I need to be able to leave the game in an instant, have it still be running and come back to the game exactly as I left it.
You will need to go trough the trouble of pressing pause button when leaving it. That's just about it, really. The game's quite slow-paced, so you don't have to grant your full attention to it and you can even do other stuff while playing it (it even has a speed slider at the bottom of its main UI, so you can even slow it down and run off until production gets finished - of course, when you're looking for an intense experience, just pull the slider all the way to the right and ... Well, it's still going to be fairly slow-paced, just a lot faster during the process)

I might also add that the game is very RPG-ish, in more ways than one.

* An engaging but not overwhelming story - I want to be drawn in by the story and/or game world but not read a novel. As this will be a part-time game, I don't want to miss out on the nuances of the story as we spend far more time at my house than hers.
The storyline in Original War is precisely that. It's not very complex, but it's very interesting and engaging - the game has means of getting you invested into individual characters and it will actually ask you to make a couple of decisions throughout the campaign, influencing story in both minor and major ways further down the line.

* Must play well given the limitations of the computer and screen size.
It'll play well, I can assure you of that, I mean it ran well on over 7 years old netbook. Screen size might be a problem tho (it probably won't, but it might, depending on the resolution.) Good news is that you can change your resolution to whatever with just a little bit of tweaking. You probably won't have to.

* Must have a decent interface. Ease of starting the game is a must.
Owar has a very self-explainatory UI which also provides you with a lot of options - just take a look at the screenshots. Thanks to its ... special properties, it can actually display pretty much everything you can do, even all units you can select at any give time in a very coherent fashion.

* Must be able to be finished within a reasonable time frame, playing part-time. I have a very flexible timetable so this is difficult to quantify, but something that is 100+ hours is not what I am looking for with this game. I'm hoping for something I can finish by next payday(13 days away) in order for the "owe you one" criteria stated below :)
Let's just say that the game really isn't all that long. It all depends on how fast you tend to play of course, but I'd say about 30 hours if what you're planning is just playing trough the campaigns. I might be horribly off tho.

* To GoG or not to GoG? It doesn't have to be a GoG game but cannot require internet connection to play. I can download something and transfer it over to her computer. Given my collection of GoG RPGs and strategy games, I probably have most of the suggestions that will come up in this thread.
I'm not really sure whether you can get it anywhere but on GOG :-P

* Sell it to me and I'll "owe you one" :) I'm after a review(linked or personally written) to aid my decision. The person who chooses the game I play will be rewarded upon completion(be that the end of the game or when I get stuck/have had enough of playing it). I'll let you know in this thread which game(s) I try and will write updates on how it is going.
Right, to finish this off, I'll just link you what I have written earlier.

The only tbs I've played enough to really recommend is Eador Genesis, which while good is actually isn't that great of an idea to play if you don't have a lot of free time since it's a slow burn and the campaign is ridiculously long/drawn out. Though I suppose it's not as big an issue if you are playing in individal scenarios.

you only have 1 castle/ race no?

Defender's Quest is quite good. And you can pause the combat :D

You have a pretty good story, funny characters and tower-defence battles. Good game for in-between :)

Well, depends - yes, you can only pick to play as a single 'castle'. However, there's about 10 bazillion ways to play that single castle, including allying yourself with other races, which then in turn allow you to recruit some of their units. So yeah, don't worry - the game is incredibly varied, just not in the ways you would expect.

I saw it,
I thought there are different races (hoped..) but only some allied buildings, a bit boring if you play 10th time same castle...

If we're talking about Heroes of Might and Magic or similar then yes, playing the same castle for the 10th time is boring. But you have to understand that Eador is very untraditional in how it plays. I think example is the best thing I can do here, really:

You can play a good ruler(drastically changing units, events and tactics you use during the entire map), picking Warrior as his first hero (effectively making him your main class for the majority of the map, forcing you to cater your playstyle to accomodate for his advantages and disadvantages)

or you can play an Evil ruler, choosing Mage + Necromancy as his main class, constantly supplementing your army with new, undead units.

Or you can choose Ranger, only hiring fast moving units to allow you for rapid response and deployment on the map.

Or you can choose Commander, enabling you to have massive armies on the field, buffed by his abilities.

And guess what, at lvl 10, you can dual-class your heroes (or continue leveling in the class you have picked in the first place) - So just the way that you build your main hero and starting force can be done in 16 separate ways. You have 3 behaviour patterns for your leader, good, evil and neutral (pretty hard to pull that off), each having its own benefits and disadvantages. You have about 5 bazillion buildings in your castle, each having a unique role and functionality - and there's no way you're going to construct 'all of them', just not gonna happen. The game forces you to plan ahead, choose your approach for any given map, and then try to be as efficient as possible. It really, really does not get boring fast.

Thanks for this suggestion. I finally got round to joining the GoG Wiki :) I've added a link to my initial post to my user profile.
I started playing the Ultima games in the 80s! They were the games that got me hooked on gaming as a child :) Ultima 7 is still probably my favourite game of all time :) I have been thinking about those a bit of late...I'm just not sure I'm up for typing "name" and "job" and taking notes for this first gaming foray :)

I am after playing something that I own - I own a ton of games and have played very few of them and completed bugger all! lol I linked my GoG Wiki profile to the initial post so people can see what I own :)

I just read your review and took a look at the game, and I have to say thank you so much for this suggestion!!! Whilst I can't get it now(Kingdoms of Amalur and Prototype on sale on Amazon took the last of my funds) that game has skyrocketed to the top of my GoG wishlist. It looks and sounds brilliant! :)

So I tried Jagged Alliance 1 and for the life of me could not figure out the interface.