Well... I don’t want to berate folks as per their experiences but with all respect - I do not believe this attraction warrants a 1-star reviews only because someone showed up late for the LAST tour of the day and couldn't get in or because "the place was hard to find" (in THIS day & age - with Google directions and GPS that is practically inexcusable)
I had NO PROBLEM finding the place punching the address into my GPS unit. My wife and I drove up to the Lab (yes it IS a functional LABORATORY not a "museum" per se!) on a Saturday morning shortly before the place opened up. yes the overall area looked a bit rundown but we didn't feel that our lives were in any danger and there is a parking lot right by the place (and again to be fair - I've been in places a lot worse than THAT; sometimes when you are on the quest for historical attractions - that’s what happens)
We had, perhaps a 10-15 mins wait and afterwards got in with no problems after paying the entry fee (about $12.00 I think)
The volunteer guide took us up on the platform to see the sub (we could not believe how small it was) and we spent may be 20-25 mins up there. Yes there are no chairs available - deal with it!
Afterwards we went down and saw all the other exhibits arranged on the 1st floor incl. the famous $20.00-gold piece that saved Lt. Dixon's life at Sharpsburg. Educational experience abound and we even got to play as we sat in the life size model from the TNT movie "The Hunley" (see my avatar picture).
There are various souvenirs and clothing articles for sale if one is interested.
If you are a Civil War NUT, like I am - it’s a MUST! if you are a faithful CW scholar - you can't go wrong... I mean you are looking at THE HUNLEY for crying out loud!!! Everyone else have to make their own decisions but as with many other attractions, my humble suggestion is do your "homework" before hands and decide it this one is for you and what are you planning to get out of the experience.
All in all - it was worth the time, money and effort for us.
P.S. Those who suggested to skip the place and see the "full size replica model" in front of the Visitor's Center on Meeting St in Charleston instead - I guess the same mentality will compel one to go to EPCOT or Vegas to claim that one "saw the Eiffel Tower" or "been to Venice". NOT!!! :)