The problem is not the level itself, you would get Level 40 way to fast, too, and you would be even stronger then you are anyways.
The problem is more that you level up way too fast.
And that the enemies aren't strong enough. You also meet them pretty early, like Super Mutants or Enclave Soldiers.
While i had literally now chance at all when i first ran into Super Mutants, i walked through hordes of them later without a scratch. When you get a companion, especially Fawkes, it becomes even easier.
And Enclave Soldiers where a joke right away.

Nah i think the leveling and the difficulty is fine. Just a ton of content in the game and I'd liek tos ee it all.

Best mod? Probably Malice for Quake. It was far and away a better singleplayer game than Quake II.

The mostest greatest mod that pleased me the most of any one I've ever played is Thief 2x, an official unofficial expansion for Thief 2. Thief 2 is way up there near the top of my gaming pantheon, so to see a near professional quality expansion come out of the love, sweat and tears of 5 years of thankless work (well, not quite thankless, but still free) was quite a treat indeed:
http://www.thief2x.com/default2.asp
My favorite HL2 mod, by far, is a episodic level pack called Minerva. I can't really explain it, but something about it stood out for me. The level design was fantastic and I liked the SHODAN-like puppetmaster. It's creator has been recruited by Valve and is working on HL2: Episode 3, so it looks like chapter 2 of Minerva is never coming out:
http://www.hylobatidae.org/minerva/
My second favorite HL2 mod is Riot Act, which also captivated me because it felt so natural. Set in Nova Prospekt:
http://uoz.multiplayer.it/ra/
Last but not least, thanks to Rice's Video Plugin for the top N64 emulators, there are TEXTURE PACKS for some of my favorite N64 games, including one for OoT which makes it look like a cartoon. I'm not sure if I can link, but I've said enough for google to do my work for me.

My favorite mod of all time is one for Quake 2 called Half-Life :D

Hey yeah, that was a pretty decent mod, actually :)