A couple more thoughts:

I think the cooking instructions which come with the slow cookers are a bit deceptive. Chop everything up, throw it all in and turn it on. It doesn't usually give the same result as the pre-frying of different ingredients in order depending on their type. My usual frying order is sear the meat, remove from pan, fry onions on medium heat for about 10 minutes, add chopped garlic for a couple of minutes then remove from the pan, throw in chunks of other firm veg e.g. carrot, sweet potato, etc and fry that for about 10 minutes. Cook in slow cooker and add softer ingredients within the last half hour to an hour, e.g. spuds and anything really soft like green beans, broccoli or frozen peas for the last 10 minutes or so. Throw in chopped fresh herbs in the last couple of minutes. We have an induction stove top with a timer on one section so I can set the timer for individual frying processes, then set the timer for the slow cooking part.

My other main thought is that stews seem to need a keynote flavour e.g. red wine, or stout, or an Italian herb mix with maybe a bit of paprika, or my fave flavour mix ras el hanout, or whatever takes your fancy but stick to one flavour theme.

And, I'm not sure if I said this before but about 15 or 20 minutes before the end of cooking beef or lamb stew in a pot - timing might be different in a slow cooker - I throw in about 3/4 cup of red lentils. They are fairly small with a neutral flavour, and break down and thicken the stew juices without detracting from the main flavour, and they add some healthy fibre as an added bonus. Easy peasy. No mucking around with a wok on a Highway to Hell setting.