Unless you say "Attorney at law" an attorney is just a representative of any sort. My husband is a LAWYER and hates it when people use the term attorney to mean lawyer. So yes there is a difference. I think people like to say attorney because it sounds fancier but it really isn't.
Sorta like when professors call themselves "doctors"....doctors of what? My husband could also be a "doctor"--a doctor of law. It's all semantics!
People with JDs (just a standard law degree) can practice pretty much any type of law they choose, criminal law included.
What criminal attorneys do on a daily basis depends on where they work and whether they work as a defense attorney (for private companies) or as a public attorney (public defenders and prosecutors). Private attorneys often specialize on highly technical sub-fields of criminal law. It's not uncommon for large firms to have attorneys who do nothing more than draft memos (typically less experienced attorneys), focus on certain fields (murder, sex crimes, constitutional issues), and who deal with specialized clients.
Is it worth it - if you like it. I know that's nebulous, but there is no other way to really explain it.
The blog below is funny, depressing, and fairly accurate.