5's ok for campaign and stuff. Single map playing, not so good. Scarce resources, small maps and slow gameplay. Nothing beats III. II is awesome too, if you're into more simplistic DOS games. I don't like IV, it's different and i can appreciate the risky idea, but i don't like it.
Try King's Bounty. RPG Heroes style, single player only, real-time (no turns). Of course, battle is turn based. Beautiful graphics. Even better than upcoming HOMM6.
Actually, original King's Bounty for DOS started the whole Heroes Of Might And Magic genre. These are remakes, first one (The Legend) came in 2008, in 2009 second iteration (Armored Princess) and in 2010 Crossworlds, expansion to Armored Princess.
There's one thing in KB games that's significantly different than in HOMM - leadership. In HOMM, it's just a simple secondary skill that raises morale, in KB it's a numeric value that increases with every level up, as a reward for some completed quests, and can be boosted with artifacts, and in small extent by picking "flags" on map. Basically, if you have 2000 leadership, and each Knight demands 400 leadership, you can have a maximum of 5 Knights in your army. So, regardless of the money, you can't recruit army as you wish. You need to be a strong hero if you want to carry a strong army.
The game rocks and it rocks hard. If you ask me, HOMM lost it's huge replay value after III. There are no more huge maps with tons of heroes and resources. I've played III in multiplayer since it came out (for that fact, i've played II also since it came out, too), with a couple of friends that were also HOMM freaks, 10-12 hour sessions, incredible. None of us played V in multiplayer for more than hour or two. We've all passed campaign (and expansion campaigns) and that was nice. So HOMM todays stands more for single player, and that's where KB kicks it's major ass.
...and there are a lot of details that change or upgrade standard HOMM gameplay mechanics to better. Won't spoil any more, go and fetch it somewhere