Hump - I bought Vampire: Bloodlines and Half-Life 2 on the same day - and shelved Half-Life 2 to play Vampire first.
I enjoyed it quite a bit, about as much as KOTOR, although KOTOR was a longer game. Also, I tended to like Vampire's endgame while I didn't enjoy KOTOR's endgame as well.
Voice-acting was superb and the writing was enjoyable, with a depth that was probably about equal to KOTOR and occasionally almost like Planescape: Torment. I enjoyed the music and like many, dropped some different music into the game to vary the mood.
With that said, one has to be honest that Vampire isn't as bug-free or hassle-free as Half-Life 2 was. My system is a 2.8 Pentium-4 with 1-gig of PC3200 Mushkin memory, an ATI Radeon 9700 Pro, and Audigy 2 soundcard. The game ran fine with no sluggishness during the game itself. Also, having checked forum recommendations, I ran "flush" on the console periodically to take care of the pernicious memory leak (and recall that Planescape: Torment also had a memory leak that worsened if you played for long stretches). I had, I believe, only 2 crashes-to-desktop.
However, load times are very long, and increase with the number of save games you have (just as KOTOR did, if I recall). Half-Life 2 seems to archive them to keep only a certain number active, which helps for that game. There is also a sound stutter, just like Half-Life 2, which I encountered only while going into the Load or Save game screens while it was trying to load up those screens. As I said, actual gameplay was fine for me. Other people have not been as fortunate, and one thing I noticed from reading the various forums is that people with less than 1-gig of memory were the ones who saw the most improvement if they were able to go up to a gig.
Some complained about the combat. The game itself was similar to KOTOR in that there could be long stretches of dialogue and quest-driven sections, then bouts of combat. I personally enjoyed the combat, but partly that was because I buffed up my character's "Celerity" (think Vampire bullet-time) skill so it added a Max Payne-ish quality to it. I also played melee through almost the majority of the game and only switched to using a katana about 75% of the way through (and never went back to melee again). The game weights toward melee for at least the first half of the game and then suddenly switches to a need for firearms skill about the last quarter of the game. So it's not quite possible to play consistently one style throughout, and becomes especially combat-heavy toward the end.
As I understood from the forums, apparently the overwhelming favorite clan to play was as a Malkavian, due to their "unique" dialogue choices. I personally played as a Toreador for the Celerity and to buff up persuasion/seduction for a more dialogue-driven game.
I wouldn't compare this with Troika's Temple of Elemental Evil. TOEE had lots of bugs, broken quests, a sense of being rushed and incomplete, but most importantly just seemed to be lacking a memorable fun quality (as compared with even a combat-heavy RPG like the Icewind Dale series). I would sort of compare TOEE with Dungeon Siege in gameplay. Like I said, I'd probably compare Vampire most closely with KOTOR.