Dragon Quest X claims to be enjoyable for those who want to play alone—going so far as to dedicate two servers to single players.
But while it can technically be played without grouping, actually doing so is far from practical—at least in the beginning. To solo the first boss in the game, you need to be almost double the level that a team of players would need to be. Moreover, when playing alone, I literally could not make enough money from killing monsters to pay my inn bill (unless I ran ten minutes back to the starting town). However, when I joined a group, not only were we able to adventure pretty much indefinitely (by pooling item drops for healing) but we were also making four times the experience per kill since we could go to much higher level areas.
Around level 15, your options for soloing take a sudden, positive turn. It is at this point (about 10-15 hours in) you gain access to one of the capital cities and have the income needed to unlock taverns. Taverns allow you to recruit other players' characters into your party as NPCs while they're offline. For a moderate fee, you can rent a group of characters for a maximum of 48 hours. The downside to this is that these characters will not level up along with you, and your control over their AI is rather limited. Still, they make soloing a viable option.
That said, being in a party of other players is still the most efficient way to play. And while there is no general chat channel in Dragon Quest X, joining a party is remarkably easy as people congregate at the entrances to towns, boss areas, and dungeons if they are looking to join a group. There are also tags you can place next to your name indicating, among other things, whether you'd like to play alone or in a group (so you can find a party even if you're already in the field). Of course, the icing on the cake is that players are exceptionally friendly and polite, making it easy to find a group no matter where you are or what you're doing.