There were some great points to THJ, the instancing for private zones was a big one. Making "camps" a non issue if multiple people needed the same spot. This was a welcome alternative to the random loot rules which I have enjoyed on mischief in regards to aug drops.
AAs from low levels is great, there was a level of nostalgia i got from going 90% AA at level 15, going around and seeing old zones.
The "build" customization was a breath of fresh air. While the metas were well established, characters felt unique.
The solo aspect of it, I was on and off with. It was handy to make builds that were good solo, but I'd have liked at least a bit of 3-4 man content in which there was incentive to roll a healer based build. I feel this is where everquest live really fails in that you either need to have a group, or a raid to do anything meaningful in the current content. I think because so much of the content was unlocked to a larger portion of the player base, it retained more people. I'd like to see EQ1 bring back 12-18 man content.
EXP boosts for alts, if you had a toon greatly ahead in AAs, your alts behind on AAs got bonus exp. On the note of EXP, you could get exp in the same zone regardless of range. This worked really well in THJ as instead of establishing a camp for everyone, you split zones up into sections and everyone worked to keep theirs cleared.
EoMs, as a RNG drop which can be used to buy bigger bags, or illusions was cool.
Bards... as long as your song was on your bar, once you casted it, it was permanent. While runes in the mid levels felt OP, i like having my buffs remain even while mezzing or pulling. It worked well with the multiclass system because you had to choose what songs were important enough for your spell bar. It reminded me of the vanguard system.
Heroic stats felt like they mattered, I'm not sure if that was a change the THJ devs made or not, but getting through different breakpoints on heroic stats actually felt like it made a difference.
The devs actually cared about balance and actively took action to boost/rebalance classes and abilities. There was customer support and effort being put into the community and DBG fails on this tremendously. The fact that some classes in EQ have been stagnated for as many years as they have been, with the class balances being implemented often being ones no one has asked for just shows how out of touch the EQ1 devs can be at times.
There was talk from the THJ devs about doing a dungeon finder type system. I was really excited to see how they could have implemented this.
Lower OOC timers, keeping self buffs after a death. The dispell mechanics some bosses used where it just disabled the buff instead of erasing it was nice.
The portal travel system was superb. We have the GH in EQ1, but the THJ version was much nicer.
I would still like to see an EQ game ditch bazaar mules and let us list stuff on the bazaar without locking up an account. Especially on TLPs where if you want a trader up at all times, you need to have a seperate subscribed account.
If i could take anything from THJ and bring it to EQ1, it would be the respawn/non-respawn zone instance system, and the permanent self buff system.