I originally watched Invisible Victory as it was airing without going back and re-watching the other 3 seasons and was honestly disappointed with it. Having had the chance to go back and watch the whole lot in one go, I have to say my opinion of it has improved.
Story wise it picks up after the last season well and doesn't really do anything dramatically different. Pacing could be better, the first 8 episodes seem to be one long cliffhanger (probably what upset me when I watched it while it was airing). While the pace could have been improved, they had a lot to cram in to 12 episodes, so I can give that a pass.
The art style is consistent with the previous seasons and did not feel out of place when watching it back to back with TSR. The addition of CG on the mechs wasn't great, but by far not the worst use I have seen. Overall it gets a pass despite the average CG effort, as a lot of it does not detract from the heat of the battle.
Overall, I would say that this is a good follow up to the massive wait. Sure I would love the original studio to work on the next season, but these guys were *fine* and I really enjoyed watching it the second time through regardless of the hiccups.
