I haven't watched Den-O, but I had finished OOO and I'm keeping up with Fourze. OOO and Fourze are quite different, with OOO being a more serious and at times sober series that deals with desires, powers, and even the meaning of existence. The suits in OOO are just amazing, and since almost all the Core Medals are interchangeable, the Kamen Rider can use countless combinations which is alot of fun to watch. Even the second Rider Birth is pretty cool and complements OOO very well.

Fourze is much more light-hearted by comparison, and with the Astro Switches and various States the suits in Fourze aren't pale by comparison next to OOO. I do think the second Rider Meteor is better than Birth, but imo Birth just wasn't utilized as well as Meteor has been.

I can go on and on about the strength & weakness of each series, but I don't want to bore you. Personally, I think you can watch Fourze first, then after you caught up you can watch OOO between episodes of Fourze. I do want to warn you though, that OOO does get a bit slow in the middle (not surprisingly, both OOO and Shinkenger were written by the same writer, Kobayashi), but it has a fantastic finish that is imo even better than W's, although I like KR W the best.

MC wise, I think Eiji is the weakest of the bunch. Gentaro is an airhead and annoying and Ryotaro is a wimp, but Eiji was just there. He was bland and so hell bent on helping everyone that you never got to know anything about him.

I would like to judge things on a series-by-series basis, but it would be unfair to Fourze right now because it's not over and because endings have proven to entirely change my opinion on a series (Double's piss poor ending still pisses me off, for example :p )

Yeah, I'm not too fond about Eiji either, and the problem for him is also because the supporting characters are just more interesting than he is. Eiji is constantly outshined by Ankh, and Date as well, not to mention Cake Boss whenever he's on the screen. Plus he is just too angst-ridden that he isn't alot of fun to watch at times.

However, OOO ends on an extremely high note, and like you said W/Double has a rather poor ending, and this is the part where OOO definitely best W by comparison.

Yeah. Eiji is easily outshined by the likes of Date, Ankh, Kougami, hell, even Gotou at times.

But OOO's ending was great. I don't want to spoil it, but I loved OOO's ending. Double's ending makes the extremely emotional episodes before it feel like a joke...

See, and I remember the extremely emotional episodes, and don't really remember what happened in the very last episode. But I was still riding the emotional previous episode, so I think Double's ending was fantastic.

The problem with W's ending is that it didn't feel like an ending, more like an epilogue of the series.

Go for it! Watch Fourze! Although, I must warn you: once you start with the bug-men, you never stop.

Oh I know. I need to kill Blasterprime546 now. (just kidden pal, heh)

Double ended with Philip magically back to life.
Basically, with everything from the Museum, Ryuu and Isaka, etc, the ending was far too squeaky clean and perfect. With how status quo was restored so perfectly that it felt as if it could've been passed off as a mid-season 2 parter.

Gah dont tempt me like that.