It did make sense to have more robots as time progressed, most series I remember had 4-5 autobots and 4-5 decepticons/predacons at first, only for their number to progressively increase as episodes went by.
I think the story for the second one was pretty damn cool, it just needed a better writer and general direction (and less toilet humor). Third one instead suffers from brutal lack of pay-off and a not-exactly bright plot (Megatron sure has complicated plans).
