Endless Waltz is sort of like a movie to finish off Gundam Wing. But it's not a movie.
It is comprised of 3 OVAs (Original Video Animations – direct to DVD). Each OVA is approximately the length of a regular Gundam Wing episode (the uncut DVD episodes, of course).
WIthin the span of these 3 episodes, it manages to pull off a somewhat cliché but at the same time, reasonably well-paced storyline. There is plenty of action, and fresh, new characters to make things interesting, as well as plenty of the old favourites.
The biggest problem with Endless Waltz seems to be the Gundams themselves. Whilst the new upgrades are nice and welcome, one can only wonder how they actually came to be (that is, if you are only watching the anime. It's possible that is explained in manga or elsewhere). At the start of the first OVA, it is a year after the end of Gundam Wing, and the mobile suits are being disposed off. The Gundams are to be destroyed – sent into the sun. Later on, once they are needed again, they are rescued before reaching the sun, but are already upgraded. This begs the question: WHEN?
There is obviously no time gap between reacquiring and using the Gundams, therefore the only explanation is that they were upgraded before being destroyed. However, if they were just going to destroy them, then why would they need to be upgraded, which costs valuable resources, including time and money? This makes no sense without explanation from external sources.
Also, none of the Gundams were given their new names, even if for most of them, it was just appending “Custom” to the end. This also made it sound like they were piloting the same Gundams from the end of the Gundam Wing series, again making no sense.
The other complaint that could be said would be how rushed Endless Waltz was. Yes, it was generally well-paced, however, the arrival of the Gundams and the final battle seemed to be held off for just a bit too long, and wasn't quite as “epic” as it could have been, with the new Wing Gundam Zero stealing the show completely, and making the rest of the Gundams look pretty much useless in comparison.
Overall though, whilst one maybe skeptical about how a plethora of new characters could work in an OVA for a series as complicated as Gundam Wing, this is a very well-rounded OVA title. Unfortunately, there are just a few bits that really stop it from being the best, and it still seems to fall short of the margin that the television series of Gundam Wing set.
However, to finish the series, it is a decent conclusion. It finishes the story of Gundam Wing, but is not necessary to watch if one feels they do not wish to continue watching after the end of the television series.