Every now and again there is a fight I really want to catch, but MMA today will never recapture the magic of the old days for multiple reasons:
1. The days of matching one martial art against another are long gone. Almost every fighter is cross trained on the same mix of striking, wrestling, and submissions, which makes the fights more homogeneous and predictable.
2. Most fighters don't come into the cage balls out, ready to bang like they used to do. Fighters today take less chances and more often fight to a decision than they used to do. Taking a more conservative approach may work for the fighters, but it doesn't work as well for the consumer that is tuning in to see an exciting fight.
Some less significant points:
3. Rounds disrupt the action. Having guys fight without being "saved by the bell" was a little more exciting. I would probably prefer to see fighters go at it for 15 minutes non-stop than have breaks every 5 minutes. Imagine a 25 minute championship match with no rounds.
4. Guys having to fight multiple fights in one night was seriously interesting. I don't think I would prefer to see marquee fighters fight each other in a multi-fight, one night tournament (due to the potential for injuries), but it would be really cool to see newer fighters who want to break into the ranks have to go through old-style UFC tournaments.
5. Having no weight classes was also more exciting. Although, today I think weight classes are necessary, there might be some rare exceptions that would be interesting to see.