Reference for Algebraic Geometry

I think the best books for what you are looking for are the following:

• Kirwan - "Complex Algebraic Curves".

This is an introduction to algebraic geometry through Riemann surfaces/complex algebraic curves which does the kind of thing you want: it proves the equivalence of the different notions of genus, proves Riemann-Roch and explains differentials.

• Beltrametti et al. - "Lectures on Curves, Surfaces and Projective Varieties"

This is a new book translated and expanded from the Italian original which is highly overlooked. It develops CLASSICAL algebraic geometry using a minimal amount of commutative algebra (you barely need some notions of abstract algebra). It is developed in the most similar way to how the subject was done before the Grothendieck revolution which seems to have permeated every modern title. There you can find old definitions of genus as an "excess", a nonstandard (noncohomological) treatment of Riemann-Roch for curves, classical important examples and constructions for curves, surfaces and morphisms, and even the development of multiplicities and Bézout's theorem using old good elimination theory and proving its projective invariance arriving at the formula most modern books use to define multiplicity (and thus forgetting all classical motivation whatsoever, the dimension of a particular vector space).

• Perrin - "Algebraic Geometry"

Along with the previous two books, this wonderful title may help you do the transition to modern abstract algebraic geometry like no other. I think it is a great companion and complement to Beltrametti's for learning the basics of the modern style along the way. It has good examples and lots of (doable) exercises (like some very interesting and easy motivations for cohomology to solve conceptually geometric problems). This is a more algebraic treatment but which develops almost all needed concepts along the way and it is one of the best introductions to the language of sheaf theory in algebraic geometry without the need of schemes (but even defines finite schemes to define multiplicities, letting you understand the relationship of how Beltrametti does things and why jumping into schemes is a good idea in the end). So eventually, you end up understanding degrees, genus, Bézout and Riemann-Roch among other things through exact sequences.

• Harris - "Algebraic Geometry, A First Course"

Actually I think one cannot learn much from this book alone if it is not supplemented by standard theoretical titles like the ones above. Nevertheless it is a great source for classical examples and results which does a good job at complementing the other books as a companion. However I do not find it more useful than that as many other people do.

• Hartshorne - "Algebraic Geometry"

In my opinion one should try to learn Hartshorne's book (not to mention Liu's which is heavily less geometrically motivated) ONLY AFTER one has understood and worked through the kind of classical algebraic geometry done in Beltrametti's book and related that geometry with an algebraic foundation like in Perrin's. Hartshorne's is the best book around IF one works through almost all the exercises, but that is no easy task. He does not motivate from a classical perspective most of the constructions, definitions and results so one must be able to do so by knowing beforehand a small deal of classical geometry. Most modern standard books work through schemes and there you are leaving the world of classical geometry and entering commutative algebra with a geometric interpretation, which is what today is called "algebraic geometry". It is nevertheless a fascinating subject.

Along the way you will need to learn enough commutative algebra to understand modern algebraic geometry. For this I would recommend the pre-published version of the recent book by Kemper - "A Course in Commutative Algebra" since its originally freely downloadable draft version included lots of exercises and problems with all their solutions (the published version does not). A great book indeed for self-study if you can get it. For a much more complete reference dealing with all the material needed for Hartshorne, Eisenbud's book is the great, but lengthy and wordy, option. A nice new succinct textbook is Singh - "Basic Commutative Algebra", to use as a purely formal reference (but with doable exercises). A good geometry-motivated introduction for those titles is Reid - "Undergraduate Commutative Algebra".

It seems to me most people have forgotten what "classical" algebraic geometry really is for which you really do not need much commutative algebra. There are two kinds of people when approaching algebraic geometry: those fascinated by the algebraic/categorical modern approach, the algebrists, and those fascinated by the original very geometrical concepts and problems, the goemeters. A typical easy question for the old geometer school is "how many surfaces of degree $d$ contain a given spatial projective curve"; the algebrists do not bother about the visual geometric interpretation and just wonder "what is the dimension of the space of global sections of the degree $d$ ideal sheaf of an irreducible algebraic set of dimension 1" (which they solve trivially through an exact sequence of sheaves). The problem to me is that many modern books (and students) are completely blinded by the algebraic language/setting, and forget what geometry is about. The perfect student of algebraic geometry should care as much for, say, derived functors as for the old geometric school that started it all (above all the geometric problems that they formulated for curves, surfaces and varieties, many of which are still unsolved whereas too many students get lost in the world of schemes for too long without knowing any geometry at all).

Fulton's Algebraic Curves: An Introduction to Algebraic Geometry which is freely available seems to fit your description. I haven't started reading it yet, but I'm planning to do so shortly: I'm in a situation similar to yours.