What are some games that were awful when they were released but became awesome after developer patching, expansions, and/or community mods/patches?

Vampire the Masquerade: Bloodlines. Nigh unplayable on release due to bugs and crashes, but great after the official and community-made patches are applied.

STALKER SoC.

Buggy mess at release, as I understand it. But fairly stable now, and some of the fan-made mods are really fantastic (one of only 2 games that I actually use mods with, the other being Morrowind)

I haven't played the game yet, but I heard more than once that, Gothic 3 with community mods, has nothing in common with its original version.

Temple of Elemental Evil.

Many would likely say Neverwinter Nights 2 as well.

Oblivion?

Fallout: New Vegas.

Oblivion with several hundred mods.

Vanilla Baldur's Gate was a mediocre game with too low resolution and poor monster AI. With TuTu or BGT, plus the BG 1 NPC Project and Sword Coast Strategems mods it is a brilliant game.

PC version of Unreal Tournament 3. Sadly, it was a case of "too little, too late", and the game didn't survive the miserable state it was in at launch. When it finally became a good game, all the players had left.

One that I know is Two Worlds 1
I have not played it, but I heard people said Two Worlds is much more playable after the 1.6 patch......

I haven't actually played the BG series yet! But when I do I will play the games unmoded to experience them as the developers made them.
Low resolution is not a problem for me since I usually find that games made for 640X480 resolution are better for me in that resolution (or the widescreen equivalent, 720 X 480) since I play on tiny 15,4 inches laptop monitor. When I buy a new computer with a larger monitor I'm likely going to double that. The ideal would be to get a monitor which supports twice the resolution that I want to play in so I could avoid the annoying blur I get when playing low resolution games on LCD monitors.

For those that want to play Baldurs Gate with higher resolutions but without the new content of TuTu, there is a good guide here:
http://social.bioware.com/forum/Baldur039s-Gate-1-and-2/Baldur039s-Gate-General-Discussion-No-Spoilers-Allowed/Tutorial-Baldur039s-Gate-without-Tutu-or-BGT-but-with-updated-resolutions-3154080-1.html

When I have played through the games one or two times, I would likely want to try the TuTu experience, and the mods you listed seemed interesting, especially the Sword Coast Strategems. Since TuTu adds more options from BG2 thus potentially making the game easier(?), this mod seems like a nice counter and a very good addition for experienced players of the game.

I have some questions for the BG 1 NPC Project. How is the quality of writing in that mod? Does it fit into the game? Is the conversations too modern for a "medieval" fantasy game compared with that from the original Bioware game?
(I expect that the original Bioware characters have a modern way of thinking that would be unrealistic in say a historic medieval game. This is no problem at all since this is a fantasy game where this is perfectly acceptable. But I would not want to use a mod that makes the dialogue even more modern.)

For me the problem with the low resolution was that the playing area was so tiny. With a 22 inch monitor and a resolution of 1440X900 you get a better overview and can play faster. And the graphics look very good at high resolutions.

Using TuTu or BGT can make BG 1 easier. One thing is that using TAB highlights items on screen, so no need for pixel hunting anymore. Another thing is that some of the new classes introduced in BG 2 are too unbalanced if used in BG 1. But there are other mods you can use to balance it.

The BG 1 NPC Project is very good, and is made by several good modders. It makes BG 1 feel more like BG 2 with the NPCs having more banters, more interjections and more quests. The writing is very good and is in the same style as the vanilla game.
Not all characters are equally developed, though.
Monty and Xzar are my favourites among the characters I've tried. Never a dull moment with the Zhentils in the party.
Kivan and Coran also have lots of new stuff.

Speaking of too modern dialogue, I actually quit the NPC Project mod for Icewind Dale when one of the characters used the expression "word".

Europa Universalis. Bland at release. Four expansions later, it is outstanding.

Hearts of Iron III. Bugged and unplayable at release.

Warlords IV. Was incredibly unbalanced initially, but after several patches (including the unofficial ones) it became quite decent. Hope we will see Warlords V one day!

Sacred 2. While it's a very good game, it was buggy and unstable at release (even after a 0th day patch!), so much so that a number of unlucky players couldn't even really play it due to the constant CTDs. Also, it had rather poor resource management, leading to sudden lags, which is understandably not cool in an ARPG, especially when fighting a boss. With time, most of the bugs were fixed, and the ones left in got taken care of by a community patch.