Graphics - probably best for pre-shaders era game.
Storyline - unusual, with personalities and epic drama(c).
AI and AI Coop/Counter/Defense missions.
Universe and planets - not much, but detailed.
Music - one of rare games with dynamic music system using DirectSound patterns. Yes, Unreal has good tracker music, defining new level of demoscene integration, but that doesn't matters with only battle/non-battle stances of, in Unreal 2 there is from 3 to 5 "heat levels" for music intensity, scaling with action intensity. The music style mostly same, but technically rendered to patterns, from other hand, lower system resources required.
Sound - yes, also one of rare games with EAX HD support.
Universe - more explanation for player with protagonist stories(expaining to NeBan).
Length - Unreal 2 was planned as real set of series(like: one planed=one game with own set of missions), but was cut down and merged to current form.
Bugs - many crashes without patch, broken graphics and intro(stucks) on some of systems including most of modern. That was never fixed, same with EAX HD - often crashes on any hardware, even with software emulation, the solution is only to turn off EAX and surround sound at all.
Closer to "reality" - you run slow, your heals is low, you aren't inhuman like in Unreal 1, also, that slows down gameplay.
The Bottom Line
Thats not Unreal game you can start with. Its only for those, who completed previous games and bored of being alone human in the da... At the planet.
From this point - you will be entertained enough being marshal, acting in unreal worlds and meeting unreal creatures till unreal unhappy ending.