Yea, I got to agree that the best map is all for one. I mean, a map with every race (except Conflux, unless you choose to start as them

) is awesome, and the lastability of just that one map is incredible.
Naga Bank on the first week? I wouldn't bother with that. I always go for the Capital ASAP (get it in the second week easily

). After that, I just get the units I need.
Tell you an awesome combo I did once. I decided to only get (as Necropolis) Skeleton Warriors, Vampire Lords, Power Liches and Dread Knights. Fact is, those are the only units you really need. The rest can be stored in case of emergency.
Using this combo, I fought an enemy army that outnumbered me massively. I chased it into it's Town and pwned it, only to find out it was the town you capture in that Southern Cross map
And yes, HoMM 5 is really all Graphic, but it's sort of like Heroes 3 with lag. Nothing really worth getting. Not even worth putting on your Christmas list to Santa or Jack Black.