The fork, perhaps as expected, is sub-par. One of the indications of that is that you can hear a hiss of air pretty loudly as the fork compresses, and in general it doesn't handle large rocks or obstacles very well. On the other hand, it isn't really designed for more than small fast vibrations on a mostly smooth track, which it handles with ease.
The wheels may have been the heaviest part on the bike. Bontrager's AT-650s are basically what Trek uses on all of its mid-entry level bikes, hybrid or mountain bike, so they're accordingly of a higher weight class. Otherwise, they hold up impressively well, even after some very big hits to the rear wheel that I was sure would have whacked it out of true. And of course, Trek's color-matching is on point with their own hubs. Quick release is quickly becoming antiquated, but only recently have thru-axles become an accepted trickle-down technology so I'll give Trek a pass on this one.
This keeps the price point low and gets more riders to mountain bike, which I respect, but it also detracts from the overall package for those who want a mountain bike to, well, mountain bike, and won't be using it for weekly rail trail rides. For instance, I found the grips would often slip on the bars on all-in climbs, and a set of lock-on grips would have been an easy upgrade for Trek to fit into this price point without much hassle.
Ultimately, due mostly to its incredible value, the X-Caliber 5 is deserving of a respectable 4/5.
MSRP - $660 USD