Omega 5 is definitely worth it, and I need somebody take on my high score so I'm motivated to go back.
Oh, and FPSs on the PS2? Nope. At least, none that weren't done better on the XBox. And given your history with the Dreamcast, I'm hesitant to recommend the PS2's "Gordon Freeman on rollerskates" Half-Life port.
I kept hearing Red Faction was decent, but I can't speak first hand on that.