Is "meaningful decisions per hour" a good measure for how fun a game might be?
Meaningful decisions per hour is one of several contributory factors, not the only one.

Other important components of "fun", at least for me, include:


high ratio of meaningful decisions to total decisions
Interesting choices to make in those decisions
Interesting setting/backstory
visual appeal
link of setting/backstory/theme to mechanics.
interactivity of players.


It's important that meaningful decisions also be interesting - I find poker rather boring unless played for money (rather than just points), as the decisions are meaningful but boring. 

Note also, burying meaningful decisions amidst many minimally meaningful decisions renders the senses numb to the meaningful ones.

Likewise, I'd rather play a good game with pretty pieces than a great game with ugly ones. I could easily make a Tsuro set, for example, but it wouldn't look nor feel as nice as the "real thing," and hence would get played less. 

The setting and theme, if presented well and with mechanics that tie to it, makes a game more enjoyable. 

Interactivity of players also matters. If the game is all meaningful decisions, but my turn is neither affected by nor affects the other players, then the game is less fun than if the do to a correct degree. (Some games can be too interactive, however. An example of this, for many, is Tongiaki. In Tongiaki, each player's action can cascade to totally change the situation, so ability to plan ahead is limited.)