I recently started playing again. IMHO for the price, even the difficulties are worth it, though I'm not sure of the long-term replayability yet. It's the only game I've found covering the period.
There are some great innovations in the game, and as soon as you get used to the concept of "teams" rather than countries, things begin to make sense.
Feedback isn't good, some things just make you scratch your head, but IMHO the game excels in "feel." It's not a generic uber-risk game with colourfull names and units, the game mechanics are specifically tailored to the period and do a great job in presenting unique challenges.
I'm running on Vista (which is stated as not supported) and getting a fair amount of crashes, but with auto-save I've found it not to be too much of an inconvenience.
I would recommend starting one of the early scenarios as a team full of barbarians. That will get you used to the combat, movement and event system without having to worry about economics or recruitment. As they evolve into Kingdoms you suddenly have to move on to logistics, administration and economics, but it's near the end of the game so you can experiement and even if you mess everything up, you can't do too much damage.
The very best feature of the game is something else I haven't found anywhere else: no "I'm so huge the endgame is a waste of time" syndrome. Because of evolution you never get to the tipping point where the game becomes so easy it's a waste of time.
I just finished the 375 game, I focussed on the Huns (as they kick ass
) and watched my Huns go from unstoppable barbarians to a dying empire unable to cope with other barbarians or Eastern Rome. Just as I thought I'd "won" I found myself unable to respond to threats, pay my armies or control revolts. My empire was crumbling as game time expired. Meanwhile my other nations were in similar positions: I'd established the Suevi in Spain but couldn't go any further and lived in uneasy equlibrium with what was left of Western Rome. My Allemani had exploded and taken all of Northern France before losing bits and pieces, and constantly worrying about wars. The only Kingdom with some security were my Saxons who were about to finish of the Picts.
My only concern was that it was a little too easy to eradicate barbarians and never face them again. I suppose it's ok in the campaign game as new waves arrive, but early on, if you kill the Goths and Franks then there is a lack of migrations later in the scenario.
On the whole though, it never seemed comfortable, in fact the start of the game was easier than the mid and end. That sort of uniqueness is worth the price alone.
I hope AGEOD redoes it with the new engine, art and turn-based style. If they manage to combine the game mechanics from GI with the interface-AI and overall game improvements from their latest engine, I will be in heaven.