Review in brief: Pikmin Short Movies will be familiar to anyone who has played the Pikmin series of games (especially Pikmin 2) but non-fans won't get the full experience. I'd only consider watching it if you're a fan of the series already, and even then it's not really recommendable. It isn't bad, but it can't be said to be as clever or whimsical as the games themselves.
Review in full: This is a collection of 3 plot-independent stories involving the titular Pikmin and (to a lesser extent) Captain Olimar. It's suggested that this takes place sometime during the events of Pikmin
2, given the types of Pikmin featured and the presence of the research pod from that game.
Apparently Shigeru Miyamoto came up with the idea to make these shorts to explore the game's characters in ways that would be difficult in an actual game. Despite this Olimar isn't given any character outside of being the guy directing the Pikmin sometimes. Aside from a couple of enemies and the research pod (who also don't do anything besides the basic role they have in the game), the only characters we're left with are the Pikmin themselves.
So the exploration is with the Pikmin, right? You could say that, and the shorts definitely focus on them, but there isn't a whole lot of character exploration with them either. After watching you'd be able to make a few bullet points regarding the base characteristics of the Pikmin as a whole, but hardly anything could be said about the individual types. Their basic abilities are shown (and the white Pikmin can spit corrosive acid for some reason) but there isn't any character behind it. A blue Pikmin could wake up as a yellow Pikmin one day and it wouldn't act any different than it had before the change, or at least we'd be led to believe that after watching this. If building characters beyond the games was the purpose of this, then it didn't achieve its goal in the slightest.
That being said the plots of the episodes themselves, while not amazing, are still enjoyable at a base level. The humor is usually decent and the stories themselves generally make sense (though it's not exactly like the games). There's even a few things that may catch you off guard. It's still nothing worth coming back to though. It also makes references to, specifically, Pikmin 2. If you haven't played that game then these shorts will not resonate fully with you.
The animation and art quality is pretty good. It's what you'd expect from something Nintendo was involved with and there's some nice touches of detail (like individual Pikmin reactions) if you look hard enough. The music is whimsical but isn't recognizable from the games (which is a shame since they have nice music). The sound consists of a lot of clips straight out of the games, which sometimes fits and sometimes feels low-quality compared to the rest of the presentation.
Verdict: It's a standard series of computerized shorts, containing some of the quirks from the games and some oddities of its own. Nostalgia aside it isn't really special and fails to be anything other than simple humor. As a fan of Pikmin I could enjoy it somewhat, but I don't see a non-fan easily getting as much (or more pessimistically, as little) out of it as I did.