The 3 doesn't make it better. Play Commandos 2 instead.
You'll get more Commandos action if you just go back and play Commandos 2 over again, maybe with a buddy, as Commandos 3 doesn't have the previous games' cooperative multiplayer mode either. A new competitive multiplayer mode emerges, and that might actually be the best feature this game has. That's not saying a lot, either.
Commandos 3 definitely has larger levels than the previous games, but that's not necesarily a good thing, because even though it means more Germans to the slaughter, it also means more Germans to the... killing me! The AI is essentially the same as it has been for the last four iterations of the game, so not much has changed there. It's an admirable system for a stealth-action game, but Commandos 3 doesn't really leave the stealth vs. action decision up to you. Specific tasks require exact and specific maneuvers, whereas Commandos 2 I found to be more free form in terms of how you choose to engage the enemy (I've laid more than a few good traps and staged a great number of German bloodbaths in my time with Commandos 2).
Case in point: If you're thinking about playing Commandos 3, you're actually wanting to play Commandos 2, so don't waste your time thinking the 3 means it's better.