Disclaimer: I've only spent a few hours total in beta stretched over different builds, so some of the below is an extrapolation from that and not first-hand experience.
Others have said enough about the class changes, I don't really like them but could probably handle it if the rest of the game were still motivating. However ...
Epic Battles: I think comparing them to skirmishes isn't fair. Because skirmishes are still somewhat interesting in comparison, while Epic Battles feel more like a Tower Defense minigame where your character skills/attributes are rendered mostly irrelevant by the new "role" mechanics and NPCs. Sure you can still hit the enemies and heal friendlies, but any nameless Rohirrim will be more effective at it than you. That is of course due to allow upscaled lowlevel chars to compete in them, as those won't have enough useful skills and scaled character stats can vary a lot (see below). If they'd implemented this as a session play it wouldn't have made much difference (it would actually have reduced confusion I think). On top of that these things are boring by sending the same wave over and over for what feels like an eternity, no random LTs requiring special tactics. Sidequests seem interesting on paper, but it generally boils down to simply defend another spot.
Promotion system: Huge grind, and at current state the maximum number of points you can get doesn't allow you even allow you to get 50% of a single tree, which only helps you in Epic Battles in the first place. Not exactly something that would encourage me to spend a lot of time.
Reward system: Well, not much change here, gold items are removed from instances completely, and I think there was no change to the general reward system there. Epic Battle rewards are based on your achievements in that new space, but the actual items are still chosen by the RNG. Overall no improvements at all to what many consider one of the worst changes brought by RoR.
Itemization: This is what actually concerns me the most. HD will bring us a huge increase in item level (teals go from 97 in RoR to 176 in HD) and therefore stats, and all new gear has a large amount of vitality and a larger amount of your primary stat (likely reversed for tank pieces). So fully geared at 95 most people will have >3k primary stat and >2k vitality (going by stats seen on crafted guild items, balance might be a bit different for EB/instance gear). This is in total contradition to the claim of specialization from the class revamp, as glass cannon builds aren't available anymore. Glass cannons would of course be totally OP with the new item level, as can be seen by upscaled 85 gear in Epic Battles resulting in mastery values of 60-80k (coming close to 200% outgoing damage as a result). Basically this just confirms that there is no plan at all for overall balancing, esp. with now three pretty different itemization schemes (pre RoI, RoI to HD, post HD) being used in the same content (Epic Battles).
In summary, from a game mechanics POV, I see a lot of things that concern me deeply, a few things I'm not sure about yet and not much I'd consider an improvement. And that is compared to the (mechanically) relatively poor state of the current live game. I originally planned to get HD with deed TPs on launch day (so no money involved), but my beta experience (not even considering all the bugs still in the last version) convinced me to take a long break from Lotro and _maybe_ revisit it in a few months to see if things turned out better/worse/as expected.
Used to play: 85 Champ / Captain / Runekeeper / Guardian, Guild Master of everything but cooking.
Playing now: Hellcat / King Tiger / GW Panther / IS / KV-5 / M4 Sherman and more