Spoiler•My very first impression: Shit, this game is ugly. Earlier games in the series invest real heavily in their sprite art style even when other handheld Nintendo series tried to go polygonal, and the Mario and Luigi games ended up really beautiful in the process. The sprites, which are all very sprite-y, looked at the same time flat and bulbous, and delightfully squishable. See Bowser's Inside Story:


Superstar Saga:


Since Dream Team is on the 3DS, they decided to go with 3D polygons for the overworld, instead of the isometric sprite overworld of the previous games. While this does make the platforming sections easier to read (especially if you turn 3D on -- apparently depth perception makes it easier when you're trying to perceive something's depth), they ended up forsaking the lovely art style of the previous games in favor of sprites with more shadows and gradients that fit in better with a 3D background. The result looks worse:
Although the background elements still look nice and charming:


•On the other hand, the dream sections, which are 2d platforming with some 3D objects, look good. I still recommend 3D on for these sections, but that's not as necessary for gameplay.

•The general concept of this game, that Luigi is especially attuned with magical pillow people because he's really good at taking naps, is just great. Thanks for keeping up the humor, Mario and Luigi.
•Battles in Luigi's dream world are a nice change in the Mario RPG formula: Luigi's subconscious version of himself possesses Mario, powering him up, and making basic attacks get multiplied into dozens of Luigis doing the same attack. The battles end up similar yet distinct from in the overworld, it's all great.
•A part of the battles that doesn't work so well is their use of 3D. Enemies might attack from behind and you have to judge their depth to know when to jump; some attacks feature a lot of things flying past but you only have to counter the ones in the same plane as Mario, Mario in the dream world has to move back and forth to dodge things, and so on. It's a nice variation on the formula, and it makes good use of the system, but even with the 3D on it's sometimes too hard to judge the depth to know when to attack, especially when enemies run toward you from behind.
•I'm really appreciating the difficulty! Maybe it's because I'm trying to go through without grinding, but it's not trivially easy. The first boss in the dream world, against the apparent main bad guy was actually difficult. I had to restart several times, and ended up winning by thinking about the opponent and adjusting my equipment to it.
•Too many tutorials. You showed my how to use badges an hour ago. I don't need another tutorial on how to use badges. I don't need to confirm 3 times that I don't need another tutorial on how to use badges.
•This is 2013. Do we still need to be kidnapping princesses? Can't there be a female character with any agency?
•As a long time fan of the series, I appreciate the things they've brought back from Superstar Saga. I'm not talking about the nods and references to that game, but rather the design choices. Setting the game outside the Mushroom Kingdom so you can have more liberty with the design -- good. Mini-Mario -- good. Making the overworld a single contiguous space -- good. (Bowser's Inside Story kind of does this too, but only for the Bowser segments. They leave half the space on the cartridge for Bowser's insides, and they keep pulling you away from the kingdom and back to Bowser. The world ends up feeling small as a result, and there ends up seeming like no real reason to look at part of it more than once.)
•The game has achievements called Expert Challenges. I like them! Some of them get a bit repetitive (Oh, you entered a new area? Try getting 10 Excellent attacks in a row here! Oh, you found a new enemy? Try winning a battle without getting hit against this one!), but they feel unintrusive and are a nice side goal to go for while you're going through an area. For the most part you're likely to complete them during regular play without having to go grind to get them.I mentioned that I hadn't been grinding for levels, but in order to complete Expert Challenges I have been going back a bit to beat enemies I had skipped past. Winning nice equipment from them is a good bonus.