At what point did misfits go wrong?

Here is a question not asked often enough at what point did the show go wrong? Well lets start by pointing out what made the show great in season one, great characters, great powers anmd a great formula. The formula that made the show great season/series 1-2 was the main cast and the fact that curtis' old power was basically a reasonable and wether intentional or not ingenius excuse to keep the show both linier and episodic (resetting everything and having the show go back to normal so anything can happen the next day) Now the biggest problem in the long run was actually in season/series 2 where they begin to break this formula by revealing the mysterious superhoodie to be simon from the future, now that alone kinda made it hard for them to let curtis keep him power as in most situations alisha would die and curtis had that power he would reset everything (though they still could have made him keep that power but they would have to shut it off or put him in a coma somehow to make that work) Thus they ultimately started the countdown for major changes to a almost perfect formula which would promise the deaths of those two characters, and season/series 5 further insults the show as a whole by trying to say it all took place in a little bit over a year. So did they write themselves into a corner? I think yes, the problem with the show by the time of series 4 is not only is the original cast all but gone and replaced by secondary characters but curtis one of the characters who had the largest influence on the plot gets killed off in a rather stupid way. So season/series 4 had too much story not enough character, very little humor, wasted third rudy idea which was a good excuse for a interesting recurring character without hiring more actors and terrible illustration of the four horsemen. Season/series 5 Aside from its repeated crude humor via shockingly stupid moments you cant help but laugh at (ie the probation worker walking in on finn and alex after Alex just fucked him up the ass taking out his satanic power and then said "oh sorry") Was just a combination of recycled ideas and lesser versions of old powers (especially considering both Alexs normal power and reverse requires more then just physical contact to take out a power) and many, many, plot holes (my favorite is why didnt anyone from the power support group sell their powers to seth who advertised himself yet could find the support group in the first place) even further when they have some good ideas like Finn meeting a girl (Leah) as akward and pathetic as him (perhaps more so) they never mention her again as if the whole thing never happened and finally they dont even end on a full closure to the show as a whole by implying they would attempt to become super heros (which maybe the original cast's powers could have pulled off but only finn seemed capable of this in the new cast)