Heroes V - TotE is a good expansion, and an outstanding expansion in comparision to previous Heroes IV expansions.
Pros: 01 new (exciting) faction, good graphics, low system requirement, 2 upgrades for each unit, sophisticate skills/spells, random map generator
Cons: Boring campaign, Low quality voice-over, some graphical glitches, dumb AI, navigation problem
If you can, rent or try it first before the purchase, since some of the game's issues are annoying and you needs to make sure if you're ok with that.
The graphics are excellent, and probably the strongest point of the game. The system requirement is surprisingly and event will accept a motherboard-integrated video chipset (like Intel 945G). Units are fun to play around with, and some of them are very well designed (e.g. Titan).
The biggest problem is the dumb AI, which means you won't have lots of time playing solo before getting sick of the AI. For example, AI defeat treasure-keeping monsters, but never grab these treasures.
Another problem is navigation. Since the map is fully 3D and is quite large, it may take times to navigate to where you were at two turns before, for example.