Yeah, it's pretty decent. Back in the day i always used to install Eset, but then i decided i don't really need that kind of security anymore. All the things i download these days are from trusted places/uploaders so I'm not much concerned about viruses and such these days.
The point is, if you're in a similar scenario then you'll be absolutely fine with Windows Defender (previously known as Microsoft Security Essensials in earlier windows). The security is fine, updates are automatic, it doesn't cause any obvious performance slowdowns, it has all the necessary features available.
Symantic used to be good back in the day, but i haven't tried it in a long time so can't tell how well it compares to modern AVs.
Bitdefender Free is pathetic for any tech users or gamers like me. As an AV it might be great because of it's good detection rates and unobtrusive interfece, but it doesn't have ANY kind of configuration or settings at all, which literally makes it the most basic AV ever. My biggest gripe with it is the lack of an Exclusions list, which means i cannot add any kind of 'false alarm' type cracks on there, and hence it will keep deleting them... a complete d!ck of an AV IMO. lol