I know many clamor for a Han Solo character in this trilogy, but if Lucas would have kept the same tempo of seriousness through this trilogy, I think it would have succeeded. Unfortunately there is no room for humor because this trilogy is a tragedy, the republic falls and the main character goes to the darkside, what is funny about that?
Everytime Lucas attempted humor in the PT, IMO, it failed miserably. TPM had Jar Jar which ruins the movie, AOTC had C-3PO cracking one liners during the most important battle of the trilogy, and in ROTS, Lucas tried to have witty banter between ObiWan and Anakin during the rescue of Palpatine, and it just wasn't funny. Everytime they attempted humor it came out forced, and just stuck out. In the OT, Han Solo, Luke, Leia, were acting out their personalities, so when they were funny, they were just being themselves, that is why the humor in the OT is fine with people cause it doesn't override the situation.
I hate the fact that TPM is a kiddy movie, AOTC, is more of a teenage movie love story movie, and then ROTS is finally serious with a PG-13 more adult movie. It makes the trilogy feel so uneven. Now everything doesn't have to be dark like ROTS, the original SW is light-hearted movie which is far from dark, but it is not a kiddy movie, it is very adult and very funny, ROTJ is when Lucas started to go kiddy.
My biggest problem with the PT is Lucas tried to grab every age market out there and when you do that, the movies don't hold up as well years later. Is it a coincidence that for many on this forum, Star Wars & ESB are their favorites 20 years later? While ROTJ is constantly put as #3 because of the Ewoks and lack of creativity? TPM may have been loved by 5-10 year olds at the time, but 10-20 years from now, those same kids are going to look back at TPM & AOTC alot like the OT generation looks at ROTJ, it just doesn't hold up as well years down the road. They will notice all the juvenile attempts at stupid humor that detract from the movie.
I would have loved to have 6 movies in my collection for SW, for I-III being the more political & serious trilogy, while IV-VI is the funnier & adveturous trilogy. Instead I look at I-III as the political & kiddie trilogy, that is where it failed.