Make sure you’ve done the updates! I’ve heard it can be slower on older mac’s but it works very well on my 2014 mac book pro. A 3+ year old mac also won’t be able to use some of the new features. The continuity features that let your iphone/ipad work as an extension of your computer are seamless with mine and being able to use your iphone as an internet hotspot is a good feature. For those that use a lot of social media and/or icloud the integration is better. For specific problems I'd look through the apple forums for, hopefully, good feedback.
‘The negative feelings we all have can be addictive…just as the positive…it’s up to
us to decide which ones we want to choose and feed”… Pema Chodron