Some say great, some say horrible, because they are experiencing different things.
(1) Putlocker is a site that gives access to many films and old TV shows, that you can stream for free. No downside at all. (Use an adblocker, if you don't like the site's look.) However, Putlocker does not itself store those films -- it just knows where they are, and fetches them for you. If you search for a title, and it is there, and it starts playing, you have lucked out. Just enjoy.
(2) But -- if anything else happens, go away. You have lost nothing (paid nothing, registered for nothing), so you have nothing to complain about. The trouble is that lots of crooks purport to offer their films to Putlocker for streaming. So Putlocker refers you to those sites, and the crookedness begins. You will be asked to register. Why? -- if what you are going to get is supposedly free? You will be given the runaround. The film you were looking for may not be there at all. Maybe you'll be shown through a site with a virus. Whatever happens to you, don't blame Putlocker itself. Just scram out of there. Don't for a moment consider registering anywhere.
Further, at present "putlocker.is" has gone away. One or both of "putlocker. Today" or "putlocker9.com" may be a mirror of the original, or may be taking up the slack.