Zone of the Enders: The 2nd Runner (PS2)
Yoshi's Island (SNES)
Metal Gear Solid (PS1)
Metal Gear Solid 2: Sons of Liberty (PS2)
Super Mario Galaxy (Wii)
Devil May Cry (PS2)
Grand Theft Auto III (PS2)
Tekken 3 (PS1)
Space Invaders Extreme (DS)
This list does NOT imply that these games have sold the most units on the service. The "measure of pleasure" essentially denotes how much time players have dedicated to these games.
In fact, #9 on this list is actually #1 in terms of units sold going by the data provided by the Nintendo Channel*. My Pokemon Ranch has sold at least 109,000 copies on WiiWare (~$1,090,000 in pure revenue) as of April 8th.
[May 3rd edit: After realizing that I jotted down erroneous data for FF4: The After Years, I have updated the preceding paragraph to reflect which game has actually sold the most units according to the data on the Nintendo Channel.]
So without further delay, I present to you all ...
WiiWare's Top 10 "Measure of Pleasure" (as of April 8th, 2010)
1. Big Kahuna Party - 24 HRS 37 MINS
2. Dr. Mario Online Rx - 21 HRS 52 MINS
3. Final Fantasy: Crystal Chronicles: My Life as a King - 17 HRS 7 MINS
4. Texas Hold 'Em Poker - 16 HRS 27 MINS
5. Pokemon Rumble - 15 HRS 32 MINS
6. Tetris Party - 15 HRS 14 MINS
7. Final Fantasy IV: The After Years - 13 HRS 47 MINS
8. Texas Hold 'Em Tournament - 13 HRS 25 MINS
9. My Pokemon Ranch - 10 HRS 34 MINS
10. World of Goo - 10 HRS 9 MINS
And here is the data for all the other tracked WiiWare games currently on the service (32 out of 201). For data to appear on the Nintendo Channel, a minimum of 50,000 hours must be played and recorded by the service. It's one reason why the VAST majority (84%!!) of WiiWare games do not have any data available.
That spreadsheet also includes a list of what I consider to be notable absences. Essentially, they are games that currently have no data available to consumers yet are what I consider interesting, a part of a franchise or from a major publisher.
Fun fact: 11 out of 15 games published by Nintendo are currently WITHOUT their data displayed.
* (Since it is not a requirement to share all game data with Nintendo and not everyone visits the Nintendo Channel after purchasing a game in the Wii Shop Channel, there very well could be more titles that sold more than FF4: The After Years.)
Inspiration for this data-mining goes out to Stephen Totilo and his monthy Wii stats reports on Kotaku.