Yeah, the delay doesn't really effect me personally since I barely use Forge at all, but it does suck for the content creators. And you're right, the fact that Big Team Battle and Forge are both missing at release will most certainly be excuses for certain critics to dock points, not to mention the completely missing local co-op. Honestly I'll be highly surprised if Halo 5 meta's over 90 considering the missing features at release and the added microtransactions. Sales-wise releasing it early instead of delaying it to December or early 2016 is the smart thing to do, Holiday sales are crucial, but it'll most definitely effect the reviews.

What microtransactions?

What microtransactions?

The in-game currency can be bought. This is primary used for randomly filled packs of burn cards. They're primarily used in Warzone to get weapons for that specific match. 343i has a lot of convoluted systems in place so we'll just have to wait till the 27th to find out how negative the impact is on the game.

https://www.youtube.com/watch?v=eN_tD5y6k6s

Honestly, based on what I've seen I'm a bit worried that the progression will be too slow. Ready up Live opened up several Gold packs + the special Limited Edition REQ packs in a video. They seemed to be getting 2 unlockables per Gold pack (plus a bunch of one time use cards) and there are around 900 unlockables in Halo 5 with more planned to be added over time. And Gold packs are the best thing you can get once you've opened up all 14 Legendary Packs (only get those if you got the Limited or Collector's editon, or Limited Edition console).

Of course we don't know how many matches it'll take on average to get a Gold Pack yet, if we're getting Gold Packs every 3 MP games or so, 2 unlockable items per pack won't be too bad, but if it's like 10 MP games per Gold Pack, it's going to take ages to unlock everything. Hopefully 343 will be willing to adjust the unlock chances and/or points per game based on feedback after release.

Yeah, 3 arena games or 1 warzone game (Warzone games last about 3 times as long as Arena games) per Gold pack sounds about right to me. At 2 unlocks per pack and 900 unlocks that would take 1350 arena games or 450 warzone games to unlock all of the base game unlocks, and they plan to add even more unlockables via free DLC. That rate of Gold packs would provide a long enough progression path to keep people playing the game for a long time so that it doesn't have longevity issues like Halo 4, but not so slow that people get discouraged and quit.