I'm going to keep this relatively brief, but I was very excited and apprehensive about the new enhancement system, so I downloaded Lammia for the first time and checked it out. I was very surprised and satisfied by what I saw.
First, it's constantly improving. I expected to have to take Wand DC enhancements, for example, as an artificer; that's already been scrapped (which isn't updated on the DDO Wiki, where I'd been drawing info from). Some things are not working yet, but it all looks amazing so far.
Almost every PRE is being fleshed out. Is it exactly what every single player wants/expect/demands? No. I'm particularly sad over Arti's not getting UMD enhancements. But overall, they've done an amazing job with the revamp.
Classes like Clerics seem to be upset about certain PREs (for example, the Protection tree), but the truth is that the tree itself (for example, if you wanted to play a tanky cleric) is often pretty well designed (if that tree represented your focus/interest). All three trees for rogues, for example, look amazing.
The redesign seems to provide more flexibility (versus less) than many people might lead you to believe. Some builds will likely be broken. It's also extremely unlikely you will end up with the same everything you had before. But you will likely have more to work with afterward (even if it's new stuff you did not ask for) than you previously had.
Multiclass and FoTM characters are most likely to be hit the hardest by the changes in new system, which is by no means dumbed down or killing flexibility. In fact, multi-classing in this system will provide almost endless customization. If you're willing to give up a pure capstone, you can pick from so many other things to replace it. Add in the fact that many abilities are tied to class levels (evasion, paly auras, bard songs, rune arm use, etc) and not directly to enhancements, and it makes the entire system feel even deeper and more complicated.
The new enhancement system will actually multiply the number of viable, interesting options people will have in building their characters.
Finally, as far as new systems and coding goes, it seems to me that focusing on new vs. existing code is actually a big deal, but not necessarily in the way people argue. If they're able to completely rewrite older code to be cleaner and better designed, I think they should go for it. Assuming the programming team is new/better, they have a chance to replace old, buggy programming and completely short-circuit the problems they were having trouble finding/correcting.
Instead of searching for weeks to isolate a bug that's been a problem, they can rewrite the code so it functions properly (and smartly) to begin with.
I'm actually pretty excited about the new expansion, and my continued time with DDO. All of this is only my opinion, and it is not meant to convince anyone who has made up their minds about anything. But, if you weren't sure about the new enhancement system--like I was before Lamma this morning--you might want to pause before panicking. Get on Lamma yourself and check it out. As of July 4th, 2013, it looks amazing to me; really, really wonderful job Turbine!