You can change classes as often as you'd like, so there's no reason not to try out everything.
The 360 version's achievement points are all locked up in the single-player game, where you'll earn points for beating specific bosses. You'll never have to go out of your way to get them, and for beating the game's final boss in both of its forms, you'll earn the final 400 points, giving you the full thousand. Considering all of the different things you can do online and with the different classes in the game, the achievements in Phantasy Star Universe are really lazy.
The long-term action is online. Much like Guild Wars, Phantasy Star Universe's online side is instanced, so there are multiple versions of every common area. You're randomly dropped into one every time you connect, though you can switch to different servers if you're looking for specific friends. On the Xbox 360, the first two or three servers seem to remain fairly populated, but the rest are absolute ghost towns. Also, you really don't get the impression that a lot of people are playing the game online. But the common areas are really only there for commerce and grouping purposes. Up to six players can be in a party, and once you start a mission, you'll never see anyone outside of your party until the mission is complete and you head back to a common area. So don't mistake this for a massively multiplayer game. It most definitely isn't one. That sort of makes the game's monthly fee a little hard to swallow, especially when consider that other games of the same type don't require a fee. On top of all that, the game doesn't even give you a 30-day trial to decide if it's your thing or not. That's pretty weak.
The game is more open-ended online, but that's more from a lack of structure than anything else. You can meet up at mission-start points or just jump into the mission menu to see if you can find any open parties to join mid-mission. Most of the missions are really dry. You get a sentence or so of text, then you're dumped in to go kill stuff. Playing with other players is nice, but playing with strangers can lead to some annoying situations when it comes to item and experience distribution. For some reason, the player who scores the final hit on a monster gets more experience than everyone else. So you might run into players that hang back for most of a boss fight then get really aggressive at the end, hoping to score that final hit. Or you might run into shady players who kick you out of their game right before a boss dies to ensure that they get all of the loot, which appears after the boss is defeated. The game offers rules for the distribution of both common and rare items, but none of the options fix this problem. So you'll probably just want to play with friends to be safe. Of course, convincing your friends to play a game with a seemingly unnecessary monthly fee is an uphill battle.
The other benefits of online play include more active commerce. Each player has his own bedroom area, and you can transform your room into a shop to sell items for whatever price you see fit. The game has a pretty handy set of shop-searching tools, and there are already a bunch of useful shops that are open and sell common items, which lower-level players would need for relatively low prices. In addition to finding and buying items, you can also craft your own. Many of the items that drop off of dead enemies or pop out of boxes when you bust them open are materials needed to synthesize items. It's kind of an arduous process. For starters, you need a synthesis board for the item you want to make, which serves as a blueprint. The board has a limited number of uses, so you can't just buy one board and pump out the same item forever. You also need specific items to create the item you want to make, which include wood, metal, photon energy, and plenty of other things. Typically, the more exquisite the weapon or armor you're trying to make, the rarer the items needed to make it. You need to insert the board and store all of the materials inside of a friendly robot that lives in your room then set it to synthesize. After that, you need to wait. Non-consumable items actually take time to craft, which is sort of crazy. Additionally, there's a chance of failure in the process. You can feed items to your synthesis machine to help it grow in level, which will make it better at synthesizing specific types of items. But based on how many crafting materials you find when you're out adventuring, it seems like you'd be better off getting into crafting rather than selling all of your materials.
It's a better game than PSO, but after five years, that alone isn't enough.
Visually, PSU looks OK, but it doesn't really look like a modern game. While it gets by on the PlayStation 2, the Xbox 360 version doesn't look much better. It has plenty of jagged edges and a real lack of variety when it comes to the environments. Additionally, the game slows down here and there, particularly during large boss encounters, but it isn't limited to those cases. The interface is similarly dated. Although it's an improvement over Phantasy Star Online, the fact that it's better than a game released five years ago isn't an impressive or surprising feat. The game's audio is decent, but if you consider the length of time you're likely to spend playing it, the music gets very repetitive. So after 10 hours or so, you might just have to turn it off. Also, on surround-sound setups, the menu noises blare out of the center channel much louder than any of the game's other sound effects.
Although Sega has made claims about the game's post-release support with plenty of new missions planned, the game still isn't dynamic enough to support a monthly fee. It's too bad because this game can most definitely become addictive. But at its core, this is a six-player action role-playing game that has repetitive worlds and repetitive combat. PSO fans will probably appreciate the game's new setting and its somewhat streamlined gameplay, but those changes definitely don't make Phantasy Star Universe a modern game.