3rd game is my least favorite as well, but the side quests were okay IMO. You are probably gonna hate the side-quests of MM4 and MM5...
And I advise you to have a regular balanced party during MM4 and MM5. Party splits do also happen in MM4. And now that they will use their bare hands, some people will outshine the others. Having a balanced party is important.
About the secret rooms, some.of them were hard, I agree, like in Castle of Malice or so. But mostly it was still balanced IMO.
4 warriors left. And well... Hope you find them in time . MM4 is a great game, much better than 3rd.