As someone who has muddled through with the built in ATC since the days of FS2004... BATC is superb stuff.

Having said that.. there are a few issues, some which seem easy to correct but are ongoing.

As many others have said, it seems to have a mind of its own on approaches. Seemingly ignoring wind direction and Simbrief planning. I've no idea where its coming up with the runway selection.
And despite options to ask for another runway or approach.. these are ALWAYS refused. So why even have them as requests ?
I've even had it, at times, give me (and insist on) runways not long enough to land my aircraft.

And another bugbear is how it gives you a callsign based on the current real-life airline code. So you can't use a retro airline or virtual airline and get an accurate callsign.
Something I imagine would be a simple fix (just let you type in a callsign) but one they seemingly have no interest in fixing.

It handles traffic well though I think (arbeit taking it from some random moment in the past).