You can't be a referee for ten years if you are no good. The Estonian showed his experience by staying cool, he let play go on, wasn't childish about the exact place for a free kick or about the ball not lying exactly still.
There's probably a lack of clout. You have to know someone at UEFA or do some really good lobbying to get a referee in the Champions League. I guess the Estonian Football Federation lacks that. But Kaldma also showed why he never got any higher: he made a few mistakes and one really big one. He saw fouls in perfectly executed slidings for example. Refs who do that are irritating. And he awarded a penalty for a clear dive by Luis Suarez. The Ajax forward dived more than once and finally got his penalty. Kaldma was quick to point at the penalty spot. He seemed a bit afraid of the players' and audience's reactions if he again would not concede a penalty.
Ajax is a famous team, that's why I sat down to watch this match. Slavia would be beaten for sure. But Ajax turned out to have really crap players who can't even get a passing right. Don't they practice in Amsterdam? Are they too busy? Slavia's defenders had no problems at all with the Ajax forwards. But they stood no chance against the Estonian referee.