Movies before show?
 

How spoiler-y are the movies to the show? It occurred to me that the movies may be a better way to sample the quality of the series that watching the first 10 or so episodes only to realize the story really isn't going anywhere like I did with Wizard.

Depends on the movie, really. The older Heisei Movies up to Kabuto tell stories that are alternative plotlines mostly, while from Kiva to Wizard (minus Decade, but Decade was a mess itself xD), the movies were at least set inside the storyline somewhere, even though not all of them fit the canon perfectly. The W and Den-O movies are the ones that are tied closest to the story.
The team-ups are usually set after the series in the first part and early in the series that makes up the second part, so those contain lots of spoilers.

For Den-O, only the first 3 movies really fit into the story, while afterwards Ryotaro's actor leaves and they scramble to figure out how to make sense of the Den-O movies.
Also, Den-O gets a lot of movies. :p

But yeah, from Kabuto and earlier, those movies specifically take place in an alternate universe, so they don't really spoil much.

Forgot to mention I was generally talking about the summer movies. I kinda forgot about the other Den-O stuff for a minute xD

As the others have said, everything up to the Kabuto movies are pretty much their own story (Shin, ZO, and J) or are set in an AU. Sometimes they'll feature characters that appear later in the series so you may be a lost a tiny bit from that.

Den-O, W, and Fourze are the only shows where the movies really tie into the show's plot (Decade tried, but it really didn't work). Pretty much anything else can be watched with minimal knowledge of the source show.

But try to avoid Movie War Core.

I don't think any of the movies outside of the early in the series movie war stuff would stand well as samplers. A lot of the pre Kabuto movies still require a fair knowledge of the characters from the series understand why certain characters react in those ways.

Not to mention that you might watch a movie and be blown away by the spectacular set pieces, and then you'll get to the series and realise the action will never be that good in the actual show.

Doesn't the Kabuto movie link back to the show by having the meteor disappear into the show timeline and that causes the events of the show to begin?

No. It could have worked that way but the show contradicts it a bit in later episodes. Plus the movie gives the impression of a happy, sunshine ending for that continuity.

Is this a ok place to mention how crappy the Zilla movie was and how slightly better the animated tv show was to the film it was based off

Even then, the movies are usually they're own self contained little stories that don't really effect the main series in a huge way. Of course, some movies assume you know what's happening in the show before hand.

I think W is the only show where the movies are actually part of the core series and MUST be watched with the show.

The first Den-O movie is too, to an extent.

Don't watch Blade's movie, it's spoils a lot even if it is an alternative ending. Same goes for Faiz which is also an AU but a lot of the stuff that happens in show, happens in the movie, albeit in a different way but still loadsa spoilers.

Den-o is tied to the series, so it's best to watch them after the show. (or in the case of it's first movie during the show)

Most neo-heisei stuff is tied in to the show, and aside from the three series above you can watch the early heisei stuff with no problem at all with spoilers since like some have said they're mostly AUs.