Mercenaries is way way too grindy. The devs absolutely do not have the amount grind to progress ratio tuned correctly, which is going to doom mercenaries to a much lower player base than it might otherwise enjoy. This is bound to be reflected in PvP queue times as time passes—as players begin abandoning this mode.
My opinion comes from a player who tends not to be put off by a lot of grinding to achieve goals which make a game a lot more fun to play in the end. The proof of this is that I am still here trying to build a couple strong PvP comps, despite how off putting the grind is— this response is from someone who has bought over 90 packs with gold.
I saw Rarran say (without much conviction in his voice) that he thought Mercenaries had the right amount of grind to it, but that opinion comes from someone who started with a 150 pack opening, and who probably later bought the Welcome bundle, along with some of the other bundles and deals that have been offered since the release.
The amount of grind when coupled with how lame the PvE content is (I have experienced better fantasy-based, dungeon-crawl content from games 20 years older than Mercenaries) are two huge negatives for Mercenaries. So much more could have been added to bring more of the WoW dungeon run experience to Mercenaries, along with other improvements to provide better entertainment from the PvE content.
The poor pack value combined with a serious diminishing returns issue as one opens more packs, since the packs lack duplicate protection or pity timers is really big deal too.
Nothing has been done to address these problems so far, and the hotfix did the opposite by increasing the time it takes to progress.
Personally, I had several days with a good ratio of MS encounters, followed with one bad day of around a 20% encounter rate, but despite my luck, the grind is way too f¥€#ing slow.
As far as making do with the way things are, the last two Felwood dungeons have given me the best returns for my time so far.
I accidentally started today with a normal Lord Banehollow run, and then I just kept running that dungeon on normal and heroic (depending if I needed heroic bounties) with the following results:
8 Mysterious Stranger
3 Blue Portal
1 Sabotage
5 Spud ME
I got the MS about 47 percent of the time.