I have to say, with absolute subjectivity, that this is probably the best season by far... and it's all because that it basically ignores the actual storyline for the first 6 episodes. And if this was any other anime, I'd definitely rate this much lower as it's basically filler, however because it's Fate/Kaleid, you all know why you're here. So let's continue and see why this is probably the best season. Since our lovable main cast has all been introduced and their characters outlined, this season expands their characters and gives you lots of fan service in between, making it one of the most enjoyable outof all three seasons. We get to see more of Kuro's mature, seductive and cheeky side, while Miyu opens up and has cuter interactions with Illya, with Illya staying relatively the same but it's the antics that she's thrust into and her reactions to them that seals the deal.
So overall, if you didn't like the series in the first place, you really shouldn't be watching this (let alone season 2). But if you loved Fate/Kaleid for what it is, definitely watch this, you will not be disappointed... well maybe when the story actually gets back on track, lol.