I think Lechuck lost some of his edge when he started cracking jokes in CMI. The 'slaw' scene in The Carnival of the Damned springs instantly to mind. While not a witty one liner as such it just seemed a little too silly for the Lechuck's of old.
To me he was always a serious character in SOMI and LCR with Guybrush's reaction to him being funny.
I thought he still retained some of that evil presence in CMI however, these two scenes especially:
http://www.youtube.com/watch?v=_Ar16...eature=related
http://www.youtube.com/watch?v=6p9bp...eature=related
Obviously time and writers move on so personal preferences aside I still thought CMI's Lechuck was a great character. He had the right balance of comedy and evil to still be thought of as a fearsome foe.
EMI Lechuck was let down by two things. His new evil plot being to run for Governor (oooooooo...

) and the fact he was working for Ozzie?...rubbish
TOMI I have to say (for me at least) is even more of a step in the wrong direction. It wasn't even so much to do with the new voice actor or even his lines.
It was the sheer lack of threat. Throughout the opening scene Lechuck pretty much just ignored Guybrush, allowing him to complete The Cursed Cutlass of Kaflu and also gave him enough time to untie Elaine had he chosen so.
Lechuck has been defeated by Guybrush on four seperate occasions and by now knows he's a threat to his plans. To ignore him like that and allow him to roam freely around Elaines ship just seemed dumb on his part. Also very un-Lechuck like.
This combined with the jolliest version of Lechuck's theme ever composed in a Monkey Island game and a lot didn't feel right about the old villain. Don't get me wrong, I love Michael Land's music but it just wasn't too fitting to what i've come to expect of Lechuck.
A few niggles with his lines (apart from the har-har-harrrs) were his almost child like insults at Guybrush "Yee be starting to get on me nerves Geekwood" seemed out of character, not something i'd expect from supposedly the most fearsome pirate in the Caribbean.
For the most part I was ok with his lines but he lacked the atmosphere and the sense of impending doom that I once used to associate with him.