Only really to expand on Gráinne's comment as regards the 'collecting' and 'roster development' sections - which are, as said 'distinct' although they are intrinsically linked - I would like to point you in the direction of the in-game Achievements > Battle Pets > Collect tab. There are a series of achievements called Raiding With Leashes, pretty much all of which can be completed via the auction house - if you have the gold/inclination - or by completing old raids.
I've been playing the Classic beta a little (and I do mean a little, the new Diablo season has me in its grips hard) and I can't see what the big fuss is about. It's Vanilla. That's what it is, that's what it was, that's what was expected and that's what we're getting. Sure there are bugs, upgrades some people didn't want and upgrades other people did want but didn't get, but in the greater scheme of things that's such a small part of the whole, it's barely worth talking about. So why are some people so insanely intent on ruining others' fun?
Logging in for the first time, being welcomed by THAT login screen and THAT music... You can't not be taken back if you've played Vanilla, and especially if you've played 2 years of it non-stop all day every day. I probably stayed 10 minutes in character creation just because of the music alone (and trying to get my character looking exactly as it did back then - although I wasn't a shaman then). The whole intro experience was especially amazing for me since the Tauren starting zone was my first encounter with WoW in the EU beta, and a little bit of that spark did return. But is that all Classic has to offer? A trip back in time when we were wowed by the game for the very first time?
This is something that people really need to start to understand, not just for Classic or WoW but software developement in general. Fixing a bug isn't just flipping a switch or changing a single digit. You have a machine with literally hundreds of thousands of parts, designed by dozens of different people at different times over the course of 20 and more years. You change a single thing and it might break 50 other things in very subtle ways that might not even emerge until months later (i.e. the very high M+ keys some players got at the start of BfA).
Keep in mind that these quests are optional, and are not necessary to continue leveling and capturing companions. They are also account-wide, so if you complete the quest chain on one character, you will not be able to complete it again on another. However, any progress that you've made will be saved and you can pick up where you left off in the quest chain on another character. The dailies that you've unlocked will also be accessible by all your toons.
This is definitely why we do a beta test. We can also do things like reset the realm at a busy time like 4:30pm PDT to try and find the source of a certain issue where a crocolisk is losing it’s brain due to how multiple processes are interacting and mirroring code to form a cohesive world. There were similar types of issues like this back in 2004 but we wanted to try and resolve this one before the weekend for the folks who are testing. (Blue Tracker / Official Forums)
When it comes to Classic, Blizzard's goal is to provide an authentic Vanilla experience, but they also needed to come up with technology to handle many players at launch, which is similar to sharding. While the use of this technology will be limited to the first month following launch, many players are questioning this decision and wouldn't like to see layering in the game at all.
The main topic for Classic at the moment would be whether the game is actually harder or just has more redundant activities you have to do before doing the stuff that's really fun. This is actually a good discussion to have, and not just for WoW, but gaming in general. The main sticking point for now, as most people are on (relatively) low levels is the breaks between killing mobs, especially for mana users. In the beginning it's actually refreshing having to think about what you can and can't pull, not just running into a bunch of mobs and killing them in *insert current optimal time to kill Blizzard determined is the most fun*. The food/drink breaks after a few (or even one) mobs provide time to actually look around the scenery and the mobs you're facing, and while there isn't much strategy involved at these levels, you still at least pretend to plan out how you're going to get to that quest mob without being killed by the 4 random ones surrounding them. Not being able to pull whatever mob you want, and actually having to check what mobs are there when you don't have interrupts yet (casters tend to be a nightmare) is definitely more difficult in a real way than what we have today. As a caster, having to actually think about which spells to use based on mana cost (and perhaps even using lower ranked ones) is definitely more difficult and requires more engagement with your character than we have in modern WoW.