I'm not going to post this as a full review, because I didn't test Avira deeply enough for a comprehensive judgement. However, I wanted to post my experiences anyway, because I think they speak a lot to the overall quality of the software.
I just want to relate a particular instance of me wanting to download and install a freeware application which, unfortunately, comes bundled with the OpenCandy installer. Avira treats this as potentially unwanted software, which I think is fine. An OpenCandy-infested installer will by default be quarantined (encrypted and moved to a quarantine folder so as to make it unharmful). I also support this behaviour – maybe it will get some of the developers who use these bundling services to reconsider their choice. Installers being removed on sight from a user's system can't be good for trust and reputation.
However, I'm well aware of what OpenCandy is and does, and feel confident that I can prevent it from installing anything unwanted. I need to use the software it is bundled with. I might also want to extract the installer manually in order to circumvent OpenCandy. Luckily, Avira upon its detection asks me whether I want to "Deny access" or "Ignore" the file. That would be very well, if the result wasn't the same in either case. Even when I choose to "Ignore" the detection, the file gets quarantined and disappears from the download location.
So off to the Quarantine tab of Avira, to select the freshly quarantined file and opt to "Restore" it. Avira asks for confirmation and then promptly does this – for all of a fraction of a second, before immediately another pop-up notifies me that it has detected the very same file as malware again, and gives it a .VIR extension. That's not really the point of choosing to restore the file now, is it?
I can keep doing this in a loop forever, the renamed file shows up in the Quarantine section again, and upon a restore, the file gets duplicated again and again with consecutive numbers after the .VIR. Renaming it back to .EXE doesn't do any good, Avira will immediately quarantine it again. At one point, Avira got itself so confused that it seems to have locked the file somehow. The .EXE copy remained there, but couldn't be accessed anymore. Try to just select it in Windows Explorer, and Windows Explorer will crash. Try to redownload from Firefox and overwrite the .EXE, and Firefox will crash. Try to unquarantine it from Avira, and the Avira interface will crash!
True, you could manually add exceptions for every file that you don't want to trap Avira in an endless quarantine loop. Or you could temporarily disable real-time protection altogether, which however isn't really the point of an anti-virus software. Unfortunately, both weren't possible in my case because I didn't set up the system myself, and AntiVir's configuration password, which was unknown to me, didn't let me change any of those settings. How did I end up installing the software I needed? I rebooted Windows into safe mode, re-downloaded and installed the software while AntiVir wasn't looking (i.e. running), and deleted the Avira-locked copies, too.
The fact that a feature as central as the quarantine and restore are so badly thought through and implemented, to the point of being unusable for the purpose they're supposed to fulfill, doesn't bode well for the quality of the rest of the software, so be aware of this. The fact that there is even a feature request asking AntiVir to not immediately re-detect files manually marked as false positives, tells me that I didn't encounter some freak misconfiguration, but this malfunction is actually as the program was designed.