Age of Empires Gold edition is almost identical to it's PC counterpart, graphics and sounds are identical and it's easy to play on a pocket pc.
I think you can get a demo here:
Age Of Empires (Pocket PC) - Download
I saw some screen shots of AoE 3 for the Trep 750 and it doesn't look half as good, although I haven't even been able to find a demo.
Too bad... it seems gaming is not for the Treo 750, unfortunately at this time I don't know of any better pocket pc phone so I'll just have to play solitaire
HTC Touch Pro is a lot slower and I don't care about the GPS, I saw video reviews of the Treo Pro and it seems to be a bit faster but still not as fast as the 750, not to mention it also shares the square screen, convenient for everything but gaming and videos.