OK, after mentioning some bad things about Caché ObjectScript, here are a couple of good things about Caché in general.
(That's not to say all the suckage is just the COS language, but we can come to other negatives later. This is a "positives" post.)
It's "alive" I'm starting to think that, possibly, the BEST thing about Caché is that it's a living platform in the sense that Steve Yegge talks about here.
What makes it "alive" is that the code is kept in the data-base and is interpreted (or rather, compiled on a routine-by-routine basis) so that it can be changed without the whole stop-recompile-restart cycle for the server. There is a terminal shell through which you can inspect and interact with the database and code. (Create objects, call functions etc.) It's not a great one in the Yegge sense, but it's there and useful.
Caché does not obviously have "advice" as Yegge calls it, but the system I work on does have dozens of hooks, and I think the developers must have got the idea from somewhere. Does Caché have plugins and other ways to extend it? Well, quite a lot of the innards seem to be visible (introspection) and new features like the OO language and the JSP-like CSP-pages ultimately compile down into the core language, so it is extensible.
Keeping the source-code in the database gives rise to one obvious and infuriating problem. You can't use all the ordinary file-based tools that you're used to for things like source-management, difference comparisons, backups and deployment. This is a problem that Caché shares with (comparing the sublime with the ridiculous) Smalltalk. Like Smalltalk, the whole "environment" of code and database is kept in a single large file.
Perhaps the resemblance is not wholly accidental. Caché might, in some ways, be moving to occupy a similar niche to something like Gemstone - a kind of self-contained persistent-object world. And as it does so, it may acquire further similarities to Smalltalk environments. Certainly had Intersystems taken Smalltalk as their model for an OO layer, rather than the stereotypical Visual C++ / Java development environments of the 90s, a great deal of pain might have been ameliorated. (That's something I want to come back to, here I'll just note that it is a good thing about Caché that it's a living platform and with some resemblance to Smalltalk.)
Batteries included : The environment includes, in a single standard installation, the database (obviously), the development tools, runtime environment and web-server.
That's quite handy to set up. It doesn't mean it's easy to deploy the environment, but once the environment is deployed, you have most of what you need for a web front-end and a database backend.
CSP is more or less like every other *SP (JSP, ASP, PHP etc.) You write HTML, can call out to COS on the server (interestingly at both compile-time and run-time, so I guess it's possible to do metaprogramming at compile-time, though need to try this.) and has some special tags.
There's also now a new browser-side component library called Zen, and AJAXy XMLHttpRequest communication behind the scenes. (Another thing I still need to play with.)
It's fast. Allegedly. But that's a plausible claim given how low level the data-access is. Compared to say a multi-layer system with Object-Relation Mapping library over ODBC to relational database.
It's simple. It is, actually. It's pretty simple to make stuff happen. You tend to have direct access to things rather than have to learn sophisticated frameworks, go through multiple abstraction layers etc. There's a downside to that, of course, (in flexibility and maintainability) but the value of simplicity of getting started, and building incrementally from simple prototypes shouldn't be discounted.