Last I had read, the STIX Font Project was aiming for a September 2005 release of their fonts for mathematical and scientific typesetting. They finally made a beta release on October 31, 2007. They are designed to be »Times compatible«, so I am not sure how they would look with AMS Euler. The beta release does not include LaTeX infrastructure, so I do not expect I will take the time to make a detailed comparison with Gentzen. Maybe later tonight I will try to prepare the STIX version of the table of glyphs I have been showing as I make progress.
I'm not sure I can really call it competition because there is no way I can hope to produce so many glyphs by myself, not to mention a bold weight version of all the glyphs. If I was using a more declarative approach, say using METAFONT, it would be a little easier to create the vast number of arrows and things by reusing common components. However, I have not really found a way to generate nice high resolution proofs using METAFONT. I have been kind of considering Gentzen to be a lifelong project (or at least until I get bored with it), so maybe I will eventually write something like METAFONT that is more modern.