There's much more to view engine except markup language. Few Spark features that I will miss:
- write html extensions using same markup language, not C# (macros) - I see that Razor also supports this, I hope it supports method/parameters override;
- custom tags (write _Tag.spark to use <Tag />);
- autogenerated variables like varIsFirst, varIndex, etc;
- special expression forms (?{} for conditional attributes, $!{} to skip errors, etc);
- nice master/partial layouts support, including ability to specify in partial that part of markup should be render only once in master (e.g. script includes);
- you can still have WebForms markup - great for compatibility and incremental upgrade;
- support to use both "" and '' quotes inside each other (extremely useful).
I like Spark syntax for loops/ifs more - mixing HTML <> and C# {} braces doesn't look too nice - but that's purely personal opinion.
There're very promising features in Razor, too, e.g. inline templates. Given that Spark creator was hired by Microsoft, I think there's a hope for Razor to be well written, very useful, and well supported view engine. Of course I won't re-write hundreds of my Spark views with Razor (though I did rewrite dozens of my WebForms views with Spark). But I will surely take a serious look at Razor - I only found this out from your questions, thanks - and what I see now looks promising. It doesn't compete with WebForms, of course (any view engine is better than WebForms), but it looks like a good choice for a new ASP.NET MVC project, if you haven't yet invested into another view engine too much.