"A modded xbox kicks @ss. A ps2 can play ps1 games, but a modded xbox can play arcade, nes, snes, n64, genesis, etc. You can run linux, watch divx movies, play mp3's. The possibilities expand all the time."
Basically everything you can do a PC. All those emulator games you list have been available for PCs for a long long long time. If someone is posting on this forum, I usually make it a safe assumption that they have a PC unless they state otherwise.
I decided to make a list of reasons to buy a PS2, this list I made for myself so that I could keep tabs on what I have and what I want, but here it is for you:
Action:
Blood Omen 2
BloodRayne
Castlevania: SOTN
Devil May Cry
Devil May Cry 2
Fear Effect
Fear Effect 2
Metal Gear 2
Metal Gear Solid
Metal Gear Solid 2
Onimusha
Onimusha 2
Primal
Resident Evil
Resident Evil 2
Resident Evil 3
Resident Evil: Veronica X
Rygar
Shinobi
Silent Hill
Silent Hill 2
Silent Hill 3
Soul Reaver
Soul Reaver 2
Syphon Filter
Syphon Filter 2
Syphon Filter 3
Tenchu 2
Tenchu 3
Zone of Enders 1
Zone of Enders 2
Fighting:
Battle Engine Aquila
Breath of Fire: Dragon Quarter
Capcom vs SNK
Capcom vs SNK 2
Guilty Gear X
Gundam Battle Assault
Gundam Battle Assault 2
King of Fighters '99
Marvel vs Capcom
Marvel vs Capcom 2
Tekken
Tekken 2
Tekken 3
Tekken 4
Tekken Tag Tourny
Platform:
Contra
Jak and Daxter
Megaman 8
Megaman x4
Megaman x5
Oddworld 2
Ratchet and Clank
RPG:
.Hack
Baldur's Gate
Chrono Cross
Final Fantasy 1
Final Fantasy 2
Final Fantasy 5
Final Fantasy 6
Final Fantasy 7
Final Fantasy 8
Final Fantasy 9
Final Fantasy 10
Final Fantasy 10-2
Final Fantasy 11
Final Fantasy Tactics
Kingdom Hearts
Legend of Mana
RPG Maker
Star Ocean
Star Ocean 2
Star Ocean 3
Suikoden 1
Suikoden 2
Suikoden 3
The Lost
Xenogears
Xenosaga Episode 1
Xenosaga Episode 2
Shooters:
Grand Theft Auto 3
Grand Theft Auto 3: Vice City
Red Faction
Red Faction 2
Twisted Metal
Twisted Metal 2
Twisted Metal 3
Twisted Metal 4
Twisted Metal Black
I'm sure I am missing a whole bunch, going to keep revising it until I've got a very accurate description of everything I like.
Edit: PS2 is quickly taking over the dreamcasts role of a system that has many many good and CHEAP games. I'm talking 7 dollars for a psx game and most ps2 titles that are old now are only 19.99.