If I may post my opinions...
Tsutarja: The middle evo is fine. It's actual a quality Pokemon, I'm just a little bored by it (and yes, I know that makes me sound like an arrogant Pokemon basher; but rest assured I am not). It's basically just a bigger form of Tsutarja, with only like two changes to distinguish it. It's done enough to improve upon Tsutarja, I just think don't think it is that good. But the final evo makes up for it. The final evo is fantastic. The only thing I don't like is how the body sort of pokes out of the skin, but I'll just accept that and move on.
Pokabu: By far the biggest let-down for me. Pokabu looked so promising, with it's happy piggishness and basic awesomeness. In short, I loved Pokabu like I hadn't loved a starter since Charmander. And then on September 1, my world was shattered. The evos of Pokabu were released, and I was crushed. WHAT HAPPENED?!! The middle evo is fine, it's a pig and its muscular. It looks like a Fire/Fighting, which disappoints me, but I'll gladly have a good looking evolutionary line of Fire/Fighting over a bad looking line of Fire/Dark (what I think Pokabu's line will be). Pokabu is fantastic, and his middle evo is decent. But the final evolution is the biggest deal-breaker of all time. I can't get over the fact that it seems to be wearing a monocle, oh, and also its terrible arms and the way it somehow lost all piggishness.
Mijumaru: For me, "Wotter"'s middle evo is the best of all 6 starter evos. The color scheme looks fantastic, and the design logically follows Mijumaru while actually improving on it. It looks like a solid Pokemon, with a Water/Fighting type as predicted. And then the final evo...It looks like a bad Swampert, and after staring at it for awhile in disgust, I realized my biggest problem with it: Why do Mijumaru and "Aquotter" stand on their hind-legs, while the final evo is on all fours? Also, everything else has changed. I just don't see it as a logical step up, plus I think it just sucks, so I won't pick Mijumaru. (I didn't like Mijumaru to begin with.)
Bottom Line: What was a promising batch of starters, led by the magnificent Pokabu, has been turned into a trio of iffy (at best) final evos. In two cases, the middle evo is better than the final evo.
Of course, this is all just my opinion.