Whatever you do, do not only read the Manifesto. It was designed as an agitation pamphlet rather than an as a complete exposition of his thinking, and it is almost entirely devoid of his economic thought. As other commenters here have said, Wage Labour and Capital is a good read. You may also benefit from a companion guide if you want the full picture. Capitalism: A Companion to Marx's Economy Critique by Johan Fornas is a very high quality book, and relatively new; published by Routledge.

You will not come away with a good overview (whether you are sympathetic or not) just from the Manifesto. This is not enough to learn about Marx's thought. WLaC is better, but it too does not do a deep enough dive into the peak of his thought, nor his method of exposition. Capital, with a companion guide, is your best bet.

As another commenter here said, the first chapters (even as admitted by Marx himself) are difficult to get through, mainly due to the fact that Marx uses a dialectical presentation in his work, in which the most 'core' and highly abstract concept is dealt with first, before progressing to more concrete concepts. As such, the book gets easier as it goes on.

Like others have said, "The Communist Manifesto" is the easiest entry point. My copy also has "The Eighteenth Brumaire of Louis Bonaparte" which some say is the work most descriptive of the US today. "The State and Revolution" by Lenin is a relatively easy and enlightening read as he talks about the nature of the capitalist state, the police, and other topics. "Reform or Revolution" by Rosa Luxemburg is also clarifying as it talks about why reformists have lost the thread. However, there are also many many many leftist podcasts you can listen to that can be easier to digest and will get you the basics, so that way when you read the original works later you have a baseline of understanding.

Capital is a doorstop, but I have heard that past chapter one which talks about the labor theory of value, the reading is much more breezy.

However, while some of these books are dense, even rural peasants have been able to read and metabolize these books, so don't despair!

Not, OP, and not well read in Marxist literature either (life is too short), but I can recommend The Communist Manifesto, it's short, quite lucid and of enormous historical influence (and would be worth reading for that reason alone). As you say, the interesting part is the analysis, the proposed remedies do not just look bad in hindsight, after tens of millions of dead bodies.

Wage Labour and Captital

I haven't read through it yet, but it's relatively short, and it was recommended to me as a good starter.

https://www.marxists.org/archive/marx/works/download/pdf/wag...

Capital is not a hard read. Marx prescriptions were not perfect but the problem description from back then is surprisingly accurate for todays workers

I think anything before the communist manifest is worth it. But it should always be read in context of the time of the industrial revolution and before.