I really liked this movie. It focused a bit too much on Sousuke compared to the other Go-ongers, and also lacked the Engines, but otherwise everything was handled very well, including the Goseiger's cameo - although I'd think that the Gedoushu would know about them...
It also seemed higher budget than the other recent Sentai crossover movies, including a new set for the final battle - I guess that changing it to a movie release got a higher budget?
Aside from the Shinkenger not knowing about the Gaiarks (really, they should have an idea about these monsters that even reduced one city to dust in the past), everything else fit perfectly into the continuity of both series too, there even was an explanation for the Go-ongers not staying around afterwards.
"Samurai 23" also was a great idea... The designs are messed up enough already, just go crazy with it! Although it left me wishing for a CG abomination made with the 23 mechas actually combining, rather than just multiple robots with the Shinkenger's cannon.
The engines had a random metallic effect in their voices here, kind of weird, considering how that was never used in the original series. Reminded me of Double in All Riders, but there was no reason for that "mistake" here.