The last game in the original series got the same justice on the PS2 as it did on seventh gen consoles.
Underworld continues the story where Legend left off, and the story is very good. If this had to be the end of the series it's very satisfyingly so. My greatest fear, however, was that the game would be half-assed on the PS2 and the developers would give all the attention to the seventh generation version. But right from the start, Underworld restored my faith in developers. The FMV cutscenes are excellent, and amazingly the in-game graphics are comparable to the PS3 version - this isn't a joke. Whether it's because the PS3's version's graphics are bad or the PS2 one's are very good, depends on whether you see the glass as half empty or half full.
The gameplay is very similar to Legend, but it's more non-linear. You can do more stuff now - shift along small ledges just by moving the analog stick rather than taking a risky jump, and there's an obligatory bike in one level. There's also a 'realistic' factor that makes it more believable through animations and excellent graphics - when standing near a fire in the first level, Lara will raise her arms in that direction to protect herself from the heat. After climbing out of water, Lara's clothes will be drenched. Yes, the latter also happened in Legend and Anniversary, but I never stopped being amazed at how much the developers did on the PS2 in the matter of visuals. The music is good, and the voice acting is well done. There is some minor slowdown in the gameplay of the second level (the one with the giant squid in it) but it never amounted to excessive frustration.
Of course, it's still a PS2 game, so the developers had to make some sacrifices - namely, the double auto target mode from the PS3 version isn't here. Ah well. Who wants that, anyway?
Overall, the now-bankrupt developers did a really good job with it and it's a shame the series was rebooted, though it couldn't have gone on forever obviously and over a decade is a nice long run for a series... but Underworld is a very satisfying end to the original series whichever platform you play it on.
... Except the Nintendo DS, of course.