Sorry for the late post.  Don’t have a lot to say about this puzzle.  Mostly fair, some good surfaces, the usual smattering of cryptic definitions that Rufus likes to use.

I’m not convinced by 20ac, and I don’t think I’ve come across 22ac in a dictionary.

ACROSS

1 OMNIBUS - does anyone still use this word in the sense of “vehicle”?

5 HUSSAR - (<=RASH) about US

9 CHAIN SAW

12 WORKING CLASS

15 ANTISEPTIC - a very good cryptic definition

20 QUADRANGLE - homophone of QUOD WRANGLE - as QUOD is short for, or derived from QUADRANGLE, I don;t think this clue is cryptic enough.

22 OPEN TRANSFER - I can’t find this phrase in Chambers or on onelook.com

27 CARO(USE)L
DOWN

1 (p)OUCH

3 BAN-JOIST

4 S((coa)L)ACK

6 US(AN)CE

7 SEA PASSAGE

8 REIN-STATES

11 UNWIND

13 BALLOONIST - good cryptic definition

14 STUTTERING - liked this one, too

16 PLURAL

18 MAKE GOOD - double definition, put something right and be a success

25 CLIP - as in “go at a fair clip”
 

I’ve only got time to say a few general comments on this puzzle so if anyone is stuck on any of the clues please leave a comment and I’ll do my best to help. If any of the bloggers wants to do a full review of it, please feel free.

You couldn’t really miss the thing in the centre of the grid which - being a child of the 80s - I recognised straightaway as a space invader (from the iconic arcade game). Another clue is the setter’s pseudonym: Tomohiro Nishikado was the designer of Space Invaders. There was also the thematic clue at 28/15:

(CESSATION GREEN V OR IM)* - GAME OVER - INSERT COINS.