I thought 5/3/1 was a great program. I like the short cycle lengths. All the good lifting principles are in there (eg. sub-max lifting, decent frequency [2+ times /week per muscle group], focus on major compounds, progress load over time, deload, goal/PR oriented) and Mr. Wendler spells things out clearly enough that pretty much any lifter wanting to get bigger and stronger has a good chance of success. It's quite like a 'simplify & win' routine but with emphasis placed on going all-out on just one major compound each session (still avoiding failure, but as big Jim says, "it should take some life out of you!"

and then, depending on your lifting goals, adding in assorted higher-rep accessory work as desired (there's good advice on this too).
There's plenty of helpful advice included on the 'big four' along with a range of accessory lifts along with ready-made templates to work from if you don't want to create your own. Add to that that it's written with a good dose of humour (well, it made me laugh) and you have a worthwhile purchase.
Personally, I don't think you're likely to make better gains in size and/or strength with 5/3/1 over a well planned out HST cycle, esp. if you go to triples or negatives for some strength work at the end of your HST cycle. However, 5/3/1's shorter cycle lengths can often be a useful way to schedule your training over the course of a busy year and the general change in set-up can be be very refreshing, so it gets a big thumbs up from me. I'll definitely be going back to it from time to time.