Yes the payoff for the April storyline seems incredibly unsatisfying. I have a feeling that there is meant to be more to that, or that it will be an ongoing thing, or maybe that is just wishful thinking on my part.
I do like the nod that the Technodrome is stranded at the bottom of the unspecified body of water (likely either the Atlantic ocean but I will have to watch again to see if there are any better indicators). Its a fun nod to the original animated series when the Technodrome was continually being stranded in unfortunate places, which was probably the writers' way of keeping this supposed ultimate weapon from always being a threat while keeping the Villains of the show continually present.
It will be interesting to see what they do with Kirby being a presence in the show in season 2. Traditionally April has largely been alone, her parents deceased, her sister absent and in at least one version her uncle was lost to a different world. Clearly in most incarnations her father meant something to her as she usually keeps his antiques shop running just to keep part of him alive. But that's not a part of her story this time (though I am hoping that Kirby might open a 2nd Time Around in this series). I am intrigued what they will do with April having family around (of course she had an apparent unseen Aunt) especially since the conceit of her relationship with the Turtles was that she didn't really have anyone else familiar (except for this apparent Aunt). This makes me wonder if Kirby will be killed or written out somehow, since he clearly is no longer April's MacGuffin.
Turtle character growth would be nice. Sadly Raph, while potentially the most emotionally complex character, is too often sidled with the role as the team aggressor and only occasionally shows real depth. And sadly he, Mike and Don have all settled nicely into their usual team roles. So in order to get the character growth you want, the writers are going to have to start taking these characters in new directions. Leo I think has the most room to grow, especially if he wants to get to the point where he surpasses Splinter as a martial artist, but that will take time.
And while I won't try to convince you to watch the original series, I do recommend the 2003 series. As much as I love the original Turtles, it's not known for it's depth or story. It's fun and nostalgic with kick-ass music, but unfortunately it lacks a certain maturity. the 2003 series however, has pretty good depth and while the characters aren't as dynamic as the Nick series counterparts, it does have a pretty fascinating ongoing storyline, that pulls from the source material heavily while establishing it's own canon and history. It hasn't aged as well as I would like, but I do think that it has plenty to offer anyone that is interested in the TMNT story.
However, what I look foward to the most is the fallout from the Karai revelation and seeing the relationship between Splinter and Shredder evolve. And yes I agree, more backstory!!