That's quite a broad question....
AICU- You can progress up the ladder if that's what you wish ie B5/6/7, ultimately taking on management for the dept. Other roles are things like transplant nurse, critical care outreach nurse, there are opportunities for pre-hospital work, but all of these do take time to develop towards.
In times of development....trachy care, airway management, Crit care drugs, art/picc/central lines, ecg interpretation, eventually courses like ALS, enhanced clinical skills.
In all areas you will be supported to develop your mentoring skills, leadership (programmes like the Edward Jenner Leadership Programme), there will be opportunities to conduct research/audits....ultimately you get what you put into it.
ED- Very similar in some ways, but if you like organised chaos it might be more up your alley.
You'll end up suturing/plastering, there are not really opportunities for pre-H work, they prefer paramedics over ED nurses, triaging.....and same as above re education and research.
There are opportunities for ENP (either B6/&)- Minor injuries nurse.
In both areas ACP's (Band 7/8a) are used. They have been slightly better incorporated into ED (currently) as they are accredited with RCEM and have a national competency framework. ICU....depends where you are, some units it works great, others less so....But this is years off for you, probably a decade away!
Hope that's somewhat helpful. Never be afraid to move around lots in nursing, it's one of the perks of the job and means you can get a lot of varied experience before maybe focussing more in one area.