It is according to its Wikipedia page & critics on Rotten Tomatoes.
In any event, prequal, reboot... call it whatever you want. Either way they are all basically attempts to make money from rehashing old stuff.
Can't speak on the Star Trek movies as I haven't watched them, but if you think "rehashing old stuff" applies to First Class and Days of Future Past, you haven't watched either of them. The stories of those two movies, cast, etc, are completely different than the original trilogy.
First Class was a clear as day prequel and Days of Future Past made that obvious because the original timeline of the first three movies was still intact (plus Wolverine's solo films). In order for the two of them to be reboots, the continuity of the original trilogy would have had to have been completely thrown out and disregarded. If you watched Days of Future Past at all you'd know that's clearly not the case as Days of Future Past used a good portion of the original cast (and by good portion I mean most of them, if not in full roles then in cameos like Beast, Cyclops, and Jean Grey) and specifically pointed back to the original trilogy at times (mostly with Wolverine, his connections to Stryker and Xavier).
In fact, I'd go so far as to say part of Days of Future Past's purpose was to wipe X-Men: The Last Stand and X-Men Origins: Wolverine from existence
without rebooting the series entirely. The rest of the history can stay in place (although, to be fair, we don't know a lot about the future timeline after Wolverine woke up apart from who's alive that wasn't after X3) but the two movies that screwed up certain parts of the universe can be thrown out to make way for future stuff, which I'd give at least partial credit to for why we now have a solo Deadpool film coming out since the guy with his mouth sewn shut never existed. Thank god.
On the topic itself, I wouldn't want a reboot just yet. Not with how things are going at the moment. I loved Days of Future Past and Apocalypse looks great as well (and it brings back my favorite character for more than just a mini cameo). After that we'll see where they take it. I worry about how many stories they can make without mixing the X-Men with another set of villains and given how they've handled pretty much everybody under the Fantastic Four umbrella, I can't say I'd be excited for an X-Men/Fantastic Four crossover in any capacity.