Quite a mixed bag with regards to service; some staff return calls regarding faults or repairs asap and are probably more helpful than you would reasonably expect. On other occasions I have called six or seven times to report the same problem, each time the member of staff saying they'll look into it and ring me back within 24 hours. On one occasion when I rang I asked why no-one ever rings me back and I was basically called a liar and that is the first time they'd spoken to me about the matter!
Fees - nothing too different to most agents, but I begrudge the fees to get the contract extended for another 6 months or year.
6 monthly inspections - plenty of notice given and very little hassle however I do think they're a little superficial, missing the important things in favour of commenting on the tidiness of the house which can be sorted in 10 minutes. I also think they're a little one sided, in favour of the landlord - items that the tenant is repsonsible for are appended with comments to the effect of 'fix this now or we'll get someone in and charge you for it', while there are no such comments against the landlords responsbilities, which i then have to chase up.
All in all I think they are paid for doing very little and represent the landlords interests far more than the tenants, but I think that can be said of any letting agent. If I had to use a letting agent again then I would (begrudgingly) use IMS again - I've dealt with worse!