Well, I don't think it's fair to judge the new penalty system yet.
For starters; it allows you to reconnect to the game. In most cases where I've dropped from a game of Dota, it was caused by a modem glitch or my PC overheating due to our lovely summer evenings. Now with Dota 2, I get the chance to reconnect to the game and don't cause my friends in my team to play against uneven odds.
As for players that DO disconnect on purpose - well - they get a rating for that and they get flagged. When they try to join another game it will throw them into a low-priority pool and it can take up to 30 minutes for them to join a game. At the moment this is only in beta, so I have a feeling that once the game is finalized the penalty system will be just and relevant to the person's behavior.
The OTHER thing which is nice about Dota 2 is that it's a LOT easier to report other players for abusive language or game-ruining tactics. Those players will, I'm sure, also be punished accordingly.
Once the leveling system comes into effect, players will be thrown into a pool with players of the same level as them, making for a MUCH better gameplay experience. No more level 5 guys trying to beat a team-stacked side consisting of level 30+ players.
Dota 2 is excellent. It's the original Dota with a complete sound and visual overhaul. PERFECT.