Yes, Interval Max is the same as Imax 1. The official name of the workout never changed, only the Catheites' informal name to distinguish it from I-Max 2 and I-max 3.
No, I-Max 3 isn't good - it's great. The interval blasts are awesome, the choreography a tad more dancy to please the more complex-choreo crowd, and the music is really, really good, especially Interval 7.
I-Max 2 is wonderfull as well.
A-Jock