Ignoring budget for a moment, since it's already been stated. But EA can designate how much goes into a pack, and should reasonably give bigger budgets for packs that require them. The horse pack shouldn't be bare because they used their budget on horse animations; they should have a bigger budget so they can make horses AND add additional content to bring the pack up to par with other EPs. (Not that we know for sure the horse pack will be lacking, but things aren't looking good for her right now.)
Anyway, here's what I believe should expect from each pack.
Expansion Packs: Offer major elements of gameplay, a wide variety of gameplay and maybe new worlds. Because it's the most expensive, it should offer the most gameplay, and its gameplay should have a lot of use. So a lot of its content should be able to carry on outside of its new world or small niche. There should be small elements of gameplay that aren't related to the main theme, but provide some nice bonus contnent.
IE, farming and seasons can be experienced in any world, sims can still do university stuff while living at home. You get exceptions like Island Living, because mermaids are pretty much useless outside of Sulani and what little gameplay the pack provides is locked to this one world.
Growing Together is a great pack because it offers content that impacts your daily gameplay (Compatibility), but has a lot of small stuff to enhance gameplay (puzzles, friendship bracelets, milestones.) It has content exclusive to San Sequoia, but it also has a lot of content that can be played anywhere and fit in with many different playstyles.
Game Packs: Focused on one or two themes instead of a wide variety, but the gameplay it focuses on should be deep. The content doesn't necessarily need to branch out into other worlds, since you're getting more specified content. You're getting less content than you would in an EP, but the content you're getting is well-developed.
Stuff Packs: Past SPs used to just be BB/CAS, and one item with a few basic interactions. But later SPs evolved into being a decent amount of CAS/BB, with one element of gameplay to focus on and develop. Like GPs, content doesn't need to have a wide reach or affect many types of gameplay styles. Sometimes we just need niche things, like kitting.
Kits: Provides some neat stuff to play with, with a very specific theme. The content isn't deep and there isn't always enough of it, but you're getting content that you really like. There should be a wide variety of themes and kit types, so more parts of the diverse and unique fandom can get content they might otherwise have gotten.
Island Living is a bad Expansion Pack, because it doesn't offer a lot of gameplay, and the gameplay we got (like mermaids) is stuck to one location. However, those limitations would be perfectly fine for a Game Pack. And this is coming from someone who loves Sulani and plays with Island Living all the time.
And here's what I expect:
Expansion Packs: Some gameplay that may or may not be deep, and may or may not work on release. A lot of BB/CAS and a small world that's mostly set dressing, to justify it being an EP. Expect reused content. Sometimes you get ____ Living packs that are geared towards one world, and those are usually the worst EPs for me.
Game Packs: The best pack type, since they tend to focus more on gameplay than anything else... Unless they're built upon pre-existing systems (like My Wedding Stories, Dream Home Decorator, or chatting with sims and collecting with StrangerVille), then they might be weak. I expect them to be more fun than EPs, since the gameplay is more developed. I expect them to be more polished upon release than EPs.
Stuff Packs: Nothing, because they're dead and gone forever. They finally became good and now they're gone.
Kits: Tbh, while there are some I love, I just see them and expect pointless cash grabs. They're less than the third of a SP's content, for half the price. We only get BB and CAS kits, and we can only hope for a gameplay kit every couple of years so they can pretend that gameplay kits aren't dead. They're neat, but they don't bring much excitement. I don't feel any excitement when I see them on a roadmap because they're so bite-sized. And they're constantly spammed, so I see them a lot - the point where it's annoying. I know I'm ranting and going off-topic, but if I have to see a new kit every other Tuesday, kits will bear witness to me complaining about them. And they still haven't paid for murdering Stuff Packs.
