1) Unlike the Punch & Judy farce of Prime Minister's Questions in the Commons, the debates have been about policy. Unfortunately, because the parties differ in degree rather than substance on key issues (economics, cuts, foreign policy, immigration) the terms of the debates were tightly circumscribed. When one candidate broke with the consensus - i.e. Nick Clegg on an amnesty for "illegal" immigrants, not renewing trident - his opponents conspired to pooh-pooh the positions and swing the debate back to the safe centre ground.
2) They may have shone a spotlight on policy, but ironically media comment has consistently reduced the debates to beauty contests. Millions of words have pondered Clegg's eye contact, Cameron's smoothness, and Brown's clunking delivery. Press spin - particularly the Tory press and Sky News - has been exposed as unashamedly partisan and propagandistic, aided and abetted by a slew of instant and easily manipulable polls.
3) Despite this, there is some evidence the debates have (temporarily) arrested the decline of mainstream politics. This was most dramatically demonstrated by the poll surge for the LibDems, but also the big rise in voter registration. Most significantly, large numbers of the group least likely to vote - the under 25s - will apparently turn out for the first time ever next Thursday. It would appear the debates have short circuited the disconnect by replicating the (TV) audience participation of the likes of Big Brother and The X-Factor. Both shows establish a relationship with the viewer by constructing participants' personalities and putting their fate in the hands of the viewer. The effect of TV votes are immediate and visible. While you can't press the red button to elect the most telegenic government (yet), the majority of people who don't normally follow politics have had their voting decision influenced by their view of the debates.
4) I have spoken to more than one person during this campaign who've said their vote was conditional on the outcome of the debates. So the genie is out of the bottle: woe betide future party leaders who elect not to participate in the Leaders' Debate. The problem now is the tendency toward personality politics is strengthened. The era of politics being showbiz for ugly people is over: the pressure to find pretty faces to front parties is almost irresistible.