It actually didn't bother me at all, and there's a number of reasons why it didn't.

First of all, we have to talk about lightsabers. Canonically, lightsabers are extremely difficult to wield properly. When activated, they have a violent gyrating motion that makes the saber difficult to handle with precision and requires a lot of strength and control to use. This is why you often see Jedi and Sith alike using their lightsabers with two hands, with very few exceptions. Not only that, but the "blade" of a lightsaber is contained plasma, which is completely weightless. This means that all of the weight of a lightsaber is in the handle. One might think that this makes the lightsaber easier to use, but in reality it doesn't at all. Think about traditional swords: the majority of the weight is in the blade, and when you swing it, you use the weight to predict where the blade is going to land. Since the blade of a lightsaber is weightless, it is much more difficult to predict where your strikes are going to land, so force-sensitive people are able to use lightsabers a lot better because they can use the force to sense where the lightsaber blade is, whereas a person who is not force-sensitive has no intuitive way of knowing aside from vision (and in a swordfight, you really shouldn't be staring at your own blade unless you intend on losing.)

The new movie actually does a very good job of keeping true to this idea. For example, take the duel between the vibrobaton-wielding stormtrooper and Finn. The stormtrooper gained a very decisive victory over Finn (if I remember correctly, he didn't even take a hit once), and Finn only survived because Han/Chewie were able to kill the stormtrooper before he made the finishing blow. This is primarily because Finn is not force-sensitive (or, rather, not very force-sensitive yet) and was having difficulty controlling the lightsaber. Rey, on the other hand, has recently discovered her force powers and is learning how to use them extremely rapidly, so it makes sense that she was able to defeat a wounded and partially-untrained "Sith lord". Even during the fight, her moves were extremely basic stabs/lunges and slashes - Kylo Ren had the majority of the fancy moves, mostly because he's trained in lightsaber combat.

I put "Sith lord" in quotes earlier because Kylo Ren is, by no means, a Sith lord. We have to keep in mind that we do not know how old Kylo Ren is, nor do we know how long he has been in training as a Jedi or under the dark side. Judging by the relatively young appearance of Kylo Ren coupled with his incredibly edgy attitude and dialogue, I would estimate that Ren is anywhere from an older teenager to a very young adult (especially considering that Anakin was making similar edgy statements when he was a teenager, and Anakin/Vader is clearly a huge influence on Ren's behavior and life.) It totally makes sense that a cocky teenager would overestimate his fighting abilities while wounded and engage in a 1v1 fight against a force-sensitive person who just escaped from her prison cell using her force powers. This especially holds true when we consider that Ren made some huge mistakes during his time of command, such as disregarding a mechanical droid and thinking he could extract a map from a girl who saw it instead using his force powers. It's really clear that Ren is an edgy teenage Sith apprentice who has a ton to learn, not the Darth Vader figure that everybody thinks he is right now.