I think Matt is partly right, Samurai and Slammer are un-reliable rides, theres no getting away from that. Samurai closed before Fright Nights due to technical problems, clearly to keep it closed for over a month during the parks busiest time is a serious fault, nothing to do with getting it ready for this year.
Slammer as you say, is Slammer, it looks like its getting major works again and if its able to run through the season from the extra work its getting than its a small sacrifice which will be worth it.
As for the water rides who knows Tidal Wave has had most of its metal work on the lift replaced, Rumbas had most of its lift replaced too, certainly not normal work. Tidal was filling up yesterday so I guess will be ready any day now.