xa_chan: But I have to admit I've spent the most time on 6. 6 is just awesome and, even if the graphisms are outdated now, it's still an excellent game, that will keep you hooked for hours and hours... If you're not afraid of fighting hordes (and I mean it literaly) of monsters and vast dungeons. 6 is a game where, in early levels, you must not be shy to retreat to the nearest town and rest. ^_^ That teaches humility, comparing to modern dungeon crawlers where you can complete a dungeon in one single go. In 6, you'll have to fight for every inch of land.
When you say big dungeons, how big are we talking here? I love Daggerfall but the dungeons in that game were way too big for my tastes.
I may go for the I-VI pack based on what people are saying. The issue is that I've bought so many games recently that I still need to get through them first (right now making my way through Fallout... fantastic game), not to mention the fact that this sale has reignited my love for HOMM 3, which I already had. That game is amazing.